remorseyoudaoicibaDictYouDict[remorse 词源字典]
remorse: [14] Remorse etymologically denotes the ‘biting’ of conscience. The word comes ultimately from medieval Latin remorsus ‘torment’, a derivative of Latin remordēre ‘bite back’, hence ‘torrnent’. This was a compound verb formed from the prefix re- ‘back, again’ and mordēre ‘bite’ (source of English morsel). The noun was used in the expression remorsus conscientiae ‘torment of conscience’, which passed into Old French as remors de conscience. English adopted this at the end of the 14th century, and by the beginning of the 15th century remorse was being used on its own in the same sense.
=> morsel[remorse etymology, remorse origin, 英语词源]
remorse (n.)youdaoicibaDictYouDict
late 14c., from Old French remors (Modern French remords), from Medieval Latin remorsum, noun use of neuter past participle of Latin remordere "to vex, disturb," literally "to bite back," from re- "back" (see re-) + mordere "to bite" (see mordant).

The sense evolution was via the Medieval Latin phrase remorsus conscientiæ (translated into Middle English as ayenbite of inwit). Middle English also had a verb, remord "to strike with remorse, touch with compassion, prick one's conscience."