'Resentment' is French for 're-feeling' — the compulsive replaying of an injury in the mind.
Bitter indignation at having been treated unfairly.
From French 'ressentiment,' from 'ressentir' (to feel strongly, to feel again), a compound of 're-' (intensive/again) and 'sentir' (to feel), from Latin 'sentīre' (to feel, to perceive, to sense). Latin 'sentīre' is traced to PIE *sent- (to go, to head for, to find one's way), which originally described physical navigation before shifting to mental perception. This root also produced Old High German 'sinnan' (to go, to travel, then to think, to meditate), German 'Sinn' (sense, meaning), Old English 'sīþ' (journey), and Lithuanian 'sintėti' (to think about). The word entered English in the early 17th century from French, initially neutral — 'to feel or perceive
Nietzsche borrowed the French 'ressentiment' (rather than the German equivalent) for a key philosophical concept: the resentment of the powerless who cannot act on their frustration, which he saw as the origin of slave morality. The French word's emphasis on 're-feeling' — compulsive repetition of the injury — captured exactly what Nietzsche meant.