conscienceyoudaoicibaDictYouDict[conscience 词源字典]
conscience: [13] Latin conscīre meant ‘be mutually aware’. It was a compound verb formed from the prefix com- ‘with, together’ and scīre ‘know’ (source of English science). To ‘know something with oneself’ implied, in a neutral sense, ‘consciousness’, but also a moral awareness, a mental differentiation between right and wrong, and hence the derived noun conscientia carried both these meanings, via Old French, into English (the more general, amoral, ‘consciousness’ died out in the 18th century).

A parallel Latin formation, using *sci-, the base of scīre, was conscius ‘aware’, acquired by English in the 17th century as conscious. Conscientious is also a 17th-century borrowing, ultimately from Latin conscientiōsus.
=> science[conscience etymology, conscience origin, 英语词源]
conscience (n.)youdaoicibaDictYouDict
early 13c., from Old French conscience "conscience, innermost thoughts, desires, intentions; feelings" (12c.), from Latin conscientia "knowledge within oneself, sense of right, a moral sense," from conscientem (nominative consciens), present participle of conscire "be (mutually) aware," from com- "with," or "thoroughly" (see com-) + scire "to know" (see science).

Probably a loan-translation of Greek syneidesis, literally "with-knowledge." Sometimes nativized in Old English/Middle English as inwit. Russian also uses a loan-translation, so-vest, "conscience," literally "with-knowledge."