The thief must have had an attack of conscience, because he returned the wallet with nothing missing from it.
… it is a politician's natural instinct to avoid taking any stand that seems controversial unless and until the voters demand it or conscience absolutely requires it. —Al Gore, An Inconvenient Truth, 2006
We like to imagine literature as the still, small voice of human conscience. It is that only rarely, however. Actively and passively, it has always borne along pernicious ideas. —Marilynne Robinson, New York Times Book Review, 15 Mar. 1987
The rat had no morals, no —conscience, no scruples, no consideration, no decency … —E. B. White, Charlotte's Web, 1952
So she had lied to him, but so had he to her, they were quits on that score and his conscience was calm. —Bernard Malamud, The Magic Barrel, (1950) 1958
Middle English, from Anglo-French, from Latin conscientia, from conscient-, consciens, present participle of conscire to be conscious, be conscious of guilt, from com- + scire to know — more at science