remorse
The first mention in the book of the word remorse, which the reader will soon discover, is an important concept. The etymology is:
remorse (n.): “intense and painful self-condemnation and penitence due to consciousness of guilt; the pain of a guilty conscience,” late 14c., from Old French remors and directly from Medieval Latin remorsum, “a biting back or in return,” the neuter past participle of Latin remordere “to vex, torment disturb,” literally “to bite back, bite again”, from re- “back, again” (see re-) + mordēre “to bite.”
The sense evolution came via the Medieval Latin phrase remorsus conscientiæ. This is Chaucer’s remors of conscience, also 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” (late 14c.), from Latin remordere.