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
词根词缀：-ase
【来源及含义】Greek: a suffix indicating an enzyme
【相关描述】From Greek diastasis and then (diast)ase, separation, interval [from dia-, through, apart, plus stasis, a standing]; an amylase that converts starch to maltose. Added to the name of a substance it usually indicates an enzyme that hydrolyzes that substance; for example, proteinases hydrolyze proteins and asparaginase hydrolyzes asparagine.
This suffix is also described as the termination denoting an enzyme, suffixed to the name of the substance (substrate) upon which the enzyme acts; e.g., phosphatase, lipase, and proteinase. It may also indicate the reaction catalyzed, e.g., decarboxylase and oxidase. Enzymes named before the convention was established generally have an -in ending; e.g., pepsin, ptyalin, and trypsin.
【同源单词】anhydrase, colipase, creatinase, cyclase, dextrase, glutaminase
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