词根：val(vail) = worth（价值）, strong（强壮的）
来源于拉丁语 valere意为worth（价值）,strong（强壮的） 变形为vail。此外，来自拉丁语的rob,fort/forc,firm,bil等也有strong的意思。
相关的词根：牛的力量很强：-vacc- 牛，来源于拉丁语vacca，如：vaccinal 疫苗的、vaccinia 牛痘。
同源词：
1. available [对某人有价值的a<ad(=to)+vail<val(=worth)]
adj. 可利用的，可使用的；有用的；可入住的；有空的：可见面的；可获得的
availability n. 有用（性）
avail v. 有助于
Many kinds of organically grown vegetables are available at this store. 在这家商店可以买到很多种有机蔬菜。
2. ambivalent [价值站在双万的ambi(=both)+val(=worth)]
adj. （两种态度、意义等）对立的，矛盾的
ambivatence n. 矛盾情绪；摇摆
I'm ambivalent about his films. They' re brilliant——but they' re too violent! 我对他的电影持矛盾的态度——电影很精彩但过于暴力！
3. invalidate [使没有价值in(= not) + val (= strong, worth)]
invalidation n. 便无效
invalidity n. 无效
invalidism n. 痛弱，虚弱
invalid adj. 无效的；(n)/(adj.) 病人；有痛的
Her research findings were invalidated by her strong personal bias. 她的研究成果因她顽固的个人偏见而变得毫无用处。
4. prevail [力量领先pre(=before)+vail<val(= strength, worth)]
vt. 占优势，战胜；普及，盛行；奏效
prevailing adj. 占优势的；普及的，流行的；有效的
prevalent adj. 普及的，流行的
prevaience n. 普及，流行
Although the team was down in the 3rd quarter ,in the end they prevailed．虽然那个队在第三局处于劣势，不过最终他们还是赢了。
5. convalesce
v.（生病后渐渐地）恢复健康 *con<com(=with)，esc(=becoming)
convalesce atter a long illness 久病之后逐渐康复
6. convalescent
adj.（病）渐愈的；恢复中的几康复期病人
convalescence n. 渐愈；恢复期
convalescent hospital （为康复期病人提供的）康复院．疗养院
7. countervail
v.与…势均力敌；抵消；补偿 *counter(=against),vail<val(=strong,strength)
countervailing duties 抵消关税
8. devaluate
v. 降低…的价值，（使）贬值 *de（=down）
devalue v. （使）贬值
devaluate the dollar 使美元贬值
9. devaluation
n. 贬值 *de(=down)
devaluation policy 贬值政策
10. equivalent
adj. 同等的 n. 同等物；相当物；意义相同的词（或符号、表达法等）*equ(=equal)
11. evaluate
v. 评价；鉴定 *e<ex(=out)
12. evaluation
n. 评价 *e<ex(=out)
13. invalid
adj.无效的 n. 患者，病人仉病弱的；（因病或伤导致的）残疾的；供病人用的
v. （因病或伤而）使退役 *in(=not)
invalidity n. 无效
invalidism n. 长期的病弱状态
invalid excuses 无效的辩解
invalid will 无效遗嘱
be invalided out of the army 因伤病而退伍
14. invaluable
adj.无法估价的，非常贵重的 *in(=intensive,not)
15. revalue
n.对…再评价；对…再估价 *re（again）
16. revaluation
n. 再评价；再估价；币值的重新调整 *re(=again)
revaluation of the German mark 量新调整德国马克的币值
17. unavailing
adj.无效的；无益的；无用的 *un（=not），a<ad(=to),vali<val(=worth)
18. undervalue
v. 低估
overvalue 高估
19. valence/valency
n. 原子价，化合价
20. valetudinarian
adj.体弱多病的；过分担心健康的
n. 体弱多病的人；过分担心健康的人
21. valiant
adj. 勇敢的，英勇的
valiant soldier 勇敢的战士
22. valid
adj. 有效的；有根据的；正当的
valid for six months 六个月内有效
raise valid objections 提出有根据的异议
23. validity
n. 正当性；有效性；效力
validate v. 使生效
24. valour
n.（特指人在战场上的）勇气；勇猛
valorous adj. 勇敢的．勇猛的
25. valuable
adj.贵重的；有价值的；有用的 (pl.)贵重物品
valuable friend 可贵的朋友
valuable discovery 有价值的发现
26. valuation
n. 评价；估价；估定的价格
27. value
n. 价值；价格；有用性
v. 评价；尊重；重视
valueless adj.没有价值的
valuer n. （财产、土地等的）估价师：评价者
value-added tax 增值税
词根：act, ag = to do, to drive （做, 驱使）
词根 ag 来自拉丁动词 agere 的词干部分，意思相当于英语的 to do （做）或to drive（驱使）。act 是个英语核心单词，其实它的前身 act 是ag的同源异形词根，来自agere（过去分词actus） 的动名词形式 actum 的词干部分，基本含义也是to do 或to drive。
同源词：
1. act
n.行为；法案；一幕
v.
同源词：
1. do something 行动：to act at once 立刻行动；2. function 起作用：The brakes wouldn't act. 刹车失录。3.take part in a play or film 扮演:Who is acting Hamlet ? 谁演哈姆雷特？
actor n.男演员；行动者
actress n.女演员
re-act v.重做，再做；重演，再演
overact v.演得过于夸张
2. action
n. 1. process of doing,or deed 行动，活动：Actions speak louder than words. 行动比语言更有说服力。
2. result of doing ,or effect 作用：the action of an acid on metal 酸对金属的作用
3. charge 诉讼：to bring an action against someone 起诉某人
actionable adj.可控诉的
3. active (act = to do 做；-ive adj.= able 会......的)
adj.able to do 活跃的,积极的：Although he is over 70,he is still active. 他虽然年过70，但依然很活跃。
activate v.使活动
activism n.[哲]能动主义；积极，活跃
activist n.活动分子，积极分子
activity n.能动性；活跃；[复]活动
4. actual（act = to do 做；-u-;-al adj.= the act or fact 表行为或事实）
adj.existing in fact;real 实际的；现实的:the actual amount of money 实际金额
actualist n.现实主义者
actuality n.事实，现在情况；现实性
actualize v.实行，使现实化
5. actuate（act = to do 做；-u-;-ate v.=to make or cause 使......）
v. cause to do 驱动，激励：What motives actuated her ? 什么动机驱使她这样做的？
actuation n.驱动，激励；开动
6. exact （ex- = out 出；act = to drive 驱使-->“to drive out;driven out 逼出来（的）”）
v.demand or obtain by force 强求，索取：He exacted obedience from his students. 他强要学生服从他。
adj.correct and without mistake 准确的，精确的：to be exact in conduct 行为一丝不苟
exacting adj.苛求的，严厉的；强索的
exaction adj.强索的；勒索；榨取
exactutude n.精确（性）；严格，严谨
7. react （re- = back 回返；act = to do 做）
v.
同源词：
1. do or act in reply 反应：She was slow to react. 她反应迟钝。
2. do against 反动，反作用：to react against oppression 反抗压迫
reaction n.反应；反作用；反动
reactor n.引起反应的人或物；[原]反应堆
reactive adj.反应的；反动的
8. interact （inter- = between 在......之间；act = to do 做 --> “to do between two things 在两者之间互动”）
v.have an effect on each other 互相作用，互相影响：All things are inter-related and interacted on each other. 一切事物都是互相联系又互相影响的。
interaction n.相互作用；相互
interactant n.[化]反应物
interactive adj.互相作用的；[计]交互的
9. transact（trans- = across or through 穿过；act = to drive 驱使 --> “to drive through 使通过”）
v. carry on;manage 执行，办理：He transacted some business at bank. 他在银行处理了一些事务。
transaction n.办理，处理；交易，业务
transactor n. 办事人，处理者
10. enact
vt.制定法律, 扮演, 颁布 *en(=in)
11. exactitude
n. 正确；精密；严正《-itude 抽象名词后缀》
12. inaction
v.不活动；懒散；怠惰《in- = not》
inactive adj.不活动的；不活泼的；懒惰的
13. agent
n.代理人；代理商；动作者；原动力（做的人）
14. agile
n.动作的敏捷；机敏
15. agitate
v. 震动；煽动
16. agitation
n.摇动；激动的状态；煽动
17. agitator
n.煽动者；游说者
18. agony
n.极大的痛苦；精神上的激动（缠绕心头）
19. cogent
adj.强有力的；使人信服的（劝动另人一起去）《co- = com- = together》
20. cogitate
v.思考；计划；设计
21. cogitable
adj.可思考的；可想象的
22. exigent
adj.急切的；紧急的；所需极多的（驱逐出去）《ex- = out;ig = act = to act》
23. prodigal
adj.浪费的；挥霍的
n.浪费者；浪子《拉丁文 prodigere = to drive forth》
词根：dox, dogma = opinion（意见）
来自希腊语的 dox 意为opinion。
（*希腊文doxa,dokein (=opinion)——英文字根字典）
同源词：
1. paradox （脱离某事物的意见 para(=beside,apart from) + dox(=opinion)
n.看似矛盾而实际（或可能）正确的说法；悖论
paradoxical adj.悖论的；矛盾的；似是而非之论的
Although an apparent paradox,when lighting is reduced in factories,productivity increases. 虽然看起来很矛盾，不过在工厂减少照明时，生产率却提高了。
2. orthodox
adj.通常的；公认的；（意见、信仰等）正统的 *ortho(=gight)
orthodoxy n.正统的信仰
orthodox beliefs 正统的信仰
orthodox behavior 正统的行为
the Orthodox Church 正教会
3. heterodox
adj.非正统的；异端的 *hetero (=other)
heterodoxy n. 非正统（学说）；异端，异说
4. doxology
n.（做礼拜时的）颂词（如“荣耀归于真神”） *log (=speech)
5. dogma
n.教条；信条；独断
6. dogmatic
adj. 教条的；武断的
7. dogmatism
n.教条主义；武断
8. doxology
n.（基督教的）颂歌；赞美诗
词根词缀：-ation, -ization, -isation
【来源及含义】Greek > Latin: a suffix; action, act, process, state, or condition; or result of doing something
【相关描述】Although there are over 1,450 word entries ending with -ation or -ization listed in this unit, there are certainly many more which exist in the English language. At any rate, this unit provides a significant number of -ation and -ization examples for you to see.
【同源单词】abarticulation, abbreviation, abdication, abdominal examination, aberration, abevacuation
词根词缀：-cide, -cides, -cidal
【来源及含义】Latin: a suffix; kill, killer; murder, to cause death, slayer; cutter; “to cut down”
【相关描述】Don’t confuse this element with the another -cide that means “to cut”; although -cide, “death”, is related to -cise, -cide, “to cut down”.
【相关词根词缀】 Related "death, dead; kill" units: lethal-; mort-; neci-; necro-; phono-; thanato-.
【同源单词】aborticide, acaricide, adulticide, algaecide, algicide, algiocide
词根词缀：columba-, columb-
【来源及含义】Latin: pigeon or dove
【相关描述】There are an estimated 300 pigeon and dove species of near passerine birds (mainly perching songbirds) in the order Columbiformes. The terms "dove" and "pigeon" are used interchangeably, although smaller species are more likely to be called doves.
【同源单词】Austrocolumbia, Columba, columbaceous, columbarian, columbarium, columbary
词根词缀：-ess
【来源及含义】Greek -issa > Late Latin -issa > Old French -esse > Middle English -esse: a suffix that forms nouns meaning a female +++, as in lioness, tigress, heiress, hostess, and sculptress
【相关描述】When -ess is added to a noun ending in -tor, -ter, the vowel before r is generally elided (eliminated or left out), as in actress (actor + -ess); and such a derivative with the ending -tress (often equivalent to French ) is usually considered a reduced form of Latin -trix, -tricem and popularly regarded as the equivalent of -tor + -ess.
In Middle English many words in -esse were adopted from French; such as, countess, duchess, mistress, and princess, or formed on nouns in -er; such as, enchantress and sorceress.
The suffix -ess is diminishing from English usage, with trends or tendencies toward avoiding any unnecessary references to gender or sexual categorizing (feminine or masculine.
The suffixes -er and -or are no longer gender-specific in modern English: an author or manager, like a doctor or writer, may be male or female, so the words authoress and manageress are considered redundant.
Some -ess words remain in use; for example, heiress and actress, although actor is being used more often now for both men and women.
【同源单词】actress, adulteress, adventuress, ancestress, auditress, aviatress
词根词缀：inter-, intero-
【来源及含义】Latin: between; among, mutually, together; on the inside, internal
【相关描述】Although abstracted from the many compounds in which it entered English, the form inter- was not generally considered a living prefix in English until the 1400s.
During the later period of Middle English many words borrowed in the Old and Middle French forms entre-, enter- began to be consciously respelled with Latin inter-; although vestiges of the older French borrowings are found in entertain and enterprise.
The living prefix inter- is now freely added to almost any element in English to create such formations with the meaning of "between" and "among". The words formed by intra- are closely related to this inter- prefix; in fact, they both apparently came from the same Latin source.
【相关词根词缀】 Related "together" units: com-; greg-; struct-. Cross references of word families related directly, or indirectly, to: "internal organs, entrails, inside": ent-; enter-; fistul-; incret-; intra-; splanchn-; viscer-.
【同源单词】ad interim, anterointernal, Caput inter nubila condit, electrical interference, electron compound, inter canem et lupum
词根词缀：-itis
【来源及含义】Greek: a suffix; inflammation, burning sensation; by extension, disease associated with inflammation
【相关描述】This suffix has come to mean "inflammation of" but originally it meant "pertaining to" or "of the". The Greek word nosos ["disease"] was either expressed or understood, although it might not be included with the basic element. For example, bursitis nosos would mean "disease of the bursa".
【同源单词】actilnoneuritis, adenitis, adrenalitis, allergyrhinitis, angioitis, angiopancreatitis
词根词缀：-oleo, -olere
【来源及含义】Latin: to destroy, to die out
【相关描述】Although it may seem difficult to accept such relationships, etymological experts agree that abolish words and adolescent words have a common ancestry.
【同源单词】abolish, abolishable, abolisher, abolishment, abolition, abolitionism