A philosophical and psychological term for deep-seated resentment, often used in discussions of Nietzsche or social theory. In everyday Japanese, 恨み (うらみ) or 反感 (はんかん) are more common.
from French ressentiment
Nietzsche argued that ressentiment is one of the origins of morality.
He harbored ressentiment toward his successful colleague.
That criticism seems to stem from ressentiment.