词根：cid, cad, cas = to fall（落下, 降临）
来源于拉丁语的cadere 意为 to fall。同义词根有来源于拉丁语的laps和来源于希腊语的pto。
同源词：
1. coincide（同时落到某物上 co<com(=togehter) + in(=upon) + cid(=fall)）(co共同+in进入+cid落下+e→共同落进)
vi. with + sth 同时发生；（想法等）一致；重合
coincidence n.同时发生；恰巧一致，巧合 (coincide[v.巧合;同时发生]+nce→n.巧合)
coincident adj.一致的；同时发生的
coincidental adj.恰巧一致的；同时发生的
Your arrival coincides with our dinner hour,so why don't you eat with us ? 你到时恰巧是我们吃晚饭的时间，那你就和我们一起吃饭吧。
2. decadence（掉到下边 de(=down) + cad(=fall)）
n.（道德等的）堕落，颓废，衰退
decay v.腐烂，衰退；（n.）腐败，衰落
decadent adj.堕落的，颓废的
Conservative religions often preach against worldly decadence. 保守的宗教常常宣扬要抵制世俗的堕落。
3. accident
n.（突发）事故；灾害，灾难；偶然（性）*ac<ad(=to ,near)
accident insurance 伤害/灾害保险
have an accident 遭遇事故
Accidents will happen. 出事是难免的
4. accidental (accident[n.意外之事,灾害]+al……的→adj.偶然的;意外的;无意中的)
adj.偶然的，意外的 *ac<ad(=to ,near)
accidentally adv. 偶然地，意外地
accidental death 意外死亡
accidental homicide 意外杀人
5. deciduous (de去掉+cid落+uous……的→使[树叶]掉下→落叶的)
adj.（树木）落叶性的；（牙、角等）定期脱落的 *de(=down)
deciduous tree 落叶树
deciduous teeth 乳齿，乳牙
6. incident (in进入+cid落下+ent→掉进来的事件)
n.事情；（政治中的）事件，变故，事变
adj.容易发生的；伴随的 *in(=into)
Political incident of the Year of Kapshin 甲申政变
risks incident to the life of a test pilot 试飞员免不了要冒的生命危险
7. incidental
adj.伴随的，附带的；次要的；易发生的 *in(=into)
incidentally adv. 附带地；偶然地
incidental expenses 额外开支，杂费
discomforts incidental to exploration in a wild coutry 在未开拓地区的探险过程中易碰到的不便之处
8. incidence (in进入+cid落下+ence表名词→掉下来的概率→发生事件的范围→影响范围)
n.发生率；（事件的）影响 *in(=into)
incidence of a disease 某种疾病的发病率
9. Occident (oc使+cid落+ent→使[太阳]落下→西方)
n.(the O ~) 西方，欧美（<-->the Orient 东方） *oc<ob(=to ,toward)
10. occidental
adj. (the O ~) 西方的，欧美的 *oc<ob(=to ,toward)
Occidental civilization 西方文明
11. recidivist
n.[律]再犯；累犯 *re(=again)
recidivism n.再犯；累犯
12. parachute
n.降落伞 v.用降落伞投下、下降 *para （=ward off），chut<cad(=fall)
parachutist n.伞兵，跳伞者
parachute troops /flares 伞兵部队/伞投照明弹
men parachuted behind the enemy lines 在敌人后方跳伞降落的人
13. cadaver
n.尸体，尸首
cadaverous adj.死尸样的；灰白的
14. caddish
adj.粗俗的，下贱的
caddish behavior 粗俗的行为
caddish trick 下流的诡计
15. cadence
n.节奏，韵律；[音]终止式
16. cascade (cas落下+cad落下+e→落下再落下→瀑布)
n.瀑布；瀑布状的东西 v. 像瀑布似的落下 *cad(=fall)
17. occasion (oc(=ob)使+cas落下+ion表名词→使……落下→事情发生)
n.（特别的事情发生的）时候，场合；机会；理由；起因；动机；盛典
v. 引起 *oc<ob(=to ,near)
on several occasions 屡次，好几次
on this occasion 借此机会
have no occasion to do 没有...理由（或必要）做...
on great occasions 在大庆/盛典时期
occasion a riot 引起骚动
18. occasional
adj.偶尔的，有时的，偶然的；临时的 *oc<ob(=to,near)
occasionally adv.偶然，有时
fine except for occasional rain 睛，间或有小雨
19. case（注意：表示容器的case 是由拉丁文capere(=to receive,to hold）演变而来的。
n.事例；情况，情形；事件，问题；患者，症状；诉讼（案件），判例；箱子，容器，盒子；[文法]格
v.装箱
casebook n.个案记录簿（法律、医学等的具体事例集）
in any case 无论如何
in nine cases out of ten 十之八九
a case of now or never 千载难逢的好时机
a hard case 棘手的问题；顽固的人
a case of influenza / smallpox 流行性感冒患者/天花患者
leading case 例案
case law 判例法
case study 事例研究
20. casual (cas落下,降临+ual……的→落下的→不是安排好的→偶然的)
adj.偶然的，意外的；不经心的；非正式的；不定期的，临时的
casually adv. 偶然地，无意地
casual wear 便装
casual remark 随口说出的话
21. casualty (casual偶然的+ty表名词→[突然]落下的事→事故)
n.不幸事故；(pl.)伤亡人员
casualty insurance 灾害保险
heavy casualties 众多死伤者
total casualties 伤亡总数
词根词缀：-agogic-, -agogue, -agog, -agogic, -agoguery, -agogy
【来源及含义】Greek: usually a suffix meaning: lead, leading, leading forth, guide, guiding; bring, take; promoting, stimulating
【相关词根词缀】Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": agon-; arch-; -crat; dom-; gov-; magist-; poten-; regi-; tyran-.
【同源单词】agogic, agogical, agogics, anagoge, anagogic, anagogical
词根词缀：agon-
【来源及含义】Greek: struggle, a contest, to contend for a prize; also, to lead, set in motion, drive, conduct, guide, govern; to do, to act; by extension, pain
【相关词根词缀】Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": -agogic; arch-; -crat; dom-; gov-; magist-; poten-; regi-; tyran-.
【同源单词】agon, agonal, agonarch, agonic, agonious, agonism
词根词缀：arch-, archi-, -arch
【来源及含义】Greek > Latin: chief, principal leader, first [in position or rank]
【相关词根词缀】Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": -agogic; agon-; -crat; dom-; gov-; magist-; poten-; regi-; tyran-.
【同源单词】archabbey, archangel, archbishop, archdeacon, archdiocese, archduchy
词根词缀：aulo-, aul-
【来源及含义】Greek: hollow way, tube, pipe; any instrument; such as, a flute
【相关词根词缀】 A cross reference of word units that are related, directly and/or indirectly, with "tube, pipe": can-, cann-; duc-, -duct (to lead, leading); fistul-; siphon-; syringo-; tub-.
【同源单词】aulophobia, aulophyte, aulophytic, aulosophile, aulostomatous, aulot
词根词缀：can-, cann-
【来源及含义】Greek > Latin: reed, pipe; the word for "reed" in Hebrew, Arabic, and Egyptian was kaneh; then the word element passed into Greek and Latin, and into the languages of western Europe
【相关词根词缀】 A cross reference of word units that are related, directly and/or indirectly, with "tube, pipe": aulo-; duc-, -duct (to lead, leading); fistul-; siphon-; syringo-; tub-.
【同源单词】canal, cane, canister, cannon, cannonarchy, cannonate
词根词缀：-crat, -cracy, -cratic, -cratism, -cratically, -cracies
【来源及含义】Greek: a suffix; to govern, to rule; government, strength, power, might, authority
【相关词根词缀】Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": -agogic; agon-; arch-; dom-; gov-; magist-; poten-; regi-; tyran-.
【同源单词】adhocracy, albocracy, aleatocracy, androcracy, androcratic, anemocracy
词根词缀：dom-, domo-, domat-, domato-
【来源及含义】Greek > Latin: house, home ["master, lord" of the house]
【相关词根词缀】Related "home; house" word units: ecdemo-; eco-; nosto-. Cross references of word families related directly, or indirectly, to: "master, lead, leading, ruler, ruling, govern": -agogic; agon-; arch-; -crat; gov-; magist-; poten-; regi-; tyran-.
【同源单词】condominial, condominium, danger, dangerous, dangerously, daunt
词根词缀：duc-, -duce, -duct, -ducent, -ductor, -duction, -ductive, -ducer, -ducement, -ducation
【来源及含义】Latin: to lead, leading; bringing; to take; to draw along or out
【相关词根词缀】 Cross references of word families related to "bear, carry, bring": -fer; ger-; later-, -lation; phoro-; port-. A cross reference of word units that are related, directly and/or indirectly, with "tube, pipe": aulo-; can-, cann-; fistul-; siphon-; syringo-; tub-.
【同源单词】abduce, abducens, abducent, abducent, abduct, abductee
词根词缀：fistul-, fistulo-, fistuli-
【来源及含义】Latin: pipe; an abnormal passage or communication, usually between two internal organs, or leading from an internal organ to the surface of the body
【相关词根词缀】Cross references of word families related directly, or indirectly, to: "internal organs, entrails, inside": ent-; enter-; incret-; inter-; intra-; splanchn-; viscer-. A cross reference of word units that are related, directly and/or indirectly, with "tube, pipe": aulo-; can-, cann-; siphon-; syringo-; tub-.
【同源单词】arteriovenous fistula, blind fistula, fistula, fistular, fistularia, fistulariidae