Conscience

Conscience is something that tells people if what they are doing is right or wrong. Having it can make people sad about what they have done. It is the sense of the moral goodness or blameworthiness of one's own conduct, intentions, or character together with a feeling of obligation to do right or be good.
Origin.
Middle English (also in the sense ‘inner thoughts or knowledge’): via Old French from Latin conscientia, from conscient- ‘being privy to’, from the verb conscire, from con- ‘with’ + scire ‘know’.