(1) 偶然
accidental: stresses chance or unexpected occurrence: any resemblance to actual persons is entirely ~.   (chance偶然: determination by irrational, uncontrollable forces由无法理解不可控的力量决定)


fortuitous: so strongly suggests chance that it often connotes entire absence of cause: believes that life is more than a series of ~ events.


casual: stresses lack of real or apparent premeditation or intent: a ~ encounter of two acquaintances.


contingent: suggests possibility of happening but stresses uncertainty and dependence on other future events: the ~ effects of a proposed amendment to the constitution.


accidental偶然: 强调偶发未预料(chance,unexpected)，fortuitous完全偶然: 强烈表示偶然，以致完全没有原因，casual偶然: 强调没有预谋目的(casual还形容人穿着等随意)，contingent可能: 强调有可能但不确定，取决于事态发展


记忆方法： 1）偶然的意思是随机发生mean happening by chance.


(2) 次要
accidental: retains its basic notion of chance occurrence but may also imply nonessential character: the essential and ~ values of an education. 翻译成“教育的本质和非本质价值”


incidental: suggests a real, sometimes a designed, relationship, but one which is secondary and nonessential: expenses ~ to the performanceof her job.


adventitious: implies a lack of essential relationship and may suggest casual addition or irrelevance: avoided elaborate designs with superfluous or ~ elements.


accidental非本质: 保留了偶然这一基本含意，但还表示非本质关系(汉语也可以说是次要，但非本质更准确)，incidental次要: 表示次要非本质关系，adventitious无关: 表示非本质，随意增加不相关的


记忆方法： 1）次要的意思是不属于真正本质属性mean not being part of the real or essential nature of something.