10. cad, cas, cid

[L]=to fall, to befall降，降临

cad，cas，cid是同源异形词根，都源于拉丁动词cadere，意思相当于to fall（降落）或to befall（降临）。其中，cad 是不定式词干，cas是动名词词干，而cid是cadere的异体cidere的不定式词干。这族同根词的数量较大。

decadent [de-=down下；cad=to fall降；-ent a.=-ing表性质→“falling down下降的”] a. falling down morally;falling into ruin堕落的；颓败的：The Ching Empire had become decadent by that time.当时清帝国已经腐败了。

▽decadence [de-;cad;-ence n.] n.衰落；颓废

case [cas=to befall降临；-e→“that which befalls降临之事”→] n. event;condition事件；情况：a typical case典型事件

casual [cas=to befall降临；-u-;-al a.=having the quality有……性质的→“having the quality of befalling, or happening by chance带有偶发性质的”→] a.① not planned偶然的：a casual meeting巧遇 ② infor-mal非正式的：casual clothing便服

▽casualty [casual;-ty n.] n.事故的伤亡者

occasion [oc-（ob-）=in the way of在……面前；cas=to befall降临；-ion n.=the state or result表状态或结果→“that which befalls in one's way降临在面前的事”→] n.① instance or case情况② favorable time, or opportunity时机；机会：as occasion serves一旦有适当的机会

▽occasional [occasion;-al a.] a.偶尔的

accident [ac-(ad-)=towards朝向；cid=to befall降临；-ent n.=thing事→“thing that befalls towards a person朝着某人降临的事”→] n. ①unexpected event意外的事；偶然的事：I met her quite by accident.我碰到她是很偶然的事。② unfortunate happening事故：traffic acci-dents交通事故

▽accidental [accident;-al a.] a.意外的；偶然的

incident [in-=on, upon在……上；cid=to befall发生；-ent n.=thing事→“thing that befalls on a particular person or happens at a particular time发生在某人身上或某个时刻的事”→] n. event, or occurence事件；事变：the July 7th Incident 七七事变

▽incidental [incident;-al a.] a.偶然的；伴随的

incidence [in-;cid;-ence n.] n.发生；发生率

coincide [co-（com-）=together共同；in-=upon在……之上；cid=to befall降临→“to befall upon together共同降临在……之上”] v. ①happen at the same time or same place（时间、空间）恰好相合：My birthday coincides with yours. 我恰好和你同一天生日。② agree;correspond一致；符合：to coincide in opinion意见相符

▽coincident [coincid(e);-ent a.] a.同时发生的；一致的

deciduous [de-=off脱离；cid=to fall降；-u-;-ous a.=having the quality有……性质的→] a. having the quality of falling off at a certain time定期脱落的：deciduous trees落叶林

occident [oc-（ob-）=down下；cid=to fall降落；-ent n.=thing connected with 表相关事物→“the direction towards which the heavenly bodies were supposed to fall down前人认为的天体降落的方向”→] n.① the west西方② the western hemisphere西半球：the Occident亚洲以西的全部国家；欧洲；欧美

▽occidental [occident;-al a.] a.西方的

decay [de-=down下；cay（cad的变形）=to fall降→] v. fall down from a state of health and excellence;rot衰退；腐朽：The old man's teeth are all decayed.这老人的牙齿全坏了。