Douglas Harper's Etymology Dictionary
1943, a word from Nietzsche, from German ressentiment, from French ressentiment (see resentment). The French word also was borrowed as obsolete English resentiment (16c.) "feeling or sense (of something); state of being deeply affected by (something); resentment."
Wiktionary
n. 1 (context obsolete English) (l/en resentment Resentment). (17th-18th c.) 2 (context chiefly social psychology English) A sense of resentment arising from suppressed feelings of envy and hatred, often leading to a frustrated sense of inferiority that may lead to various social repercussions. (from 19th c.)
Wikipedia
Ressentiment , in philosophy and psychology, is one of the forms of resentment or hostility. It is the French word for "resentment" (fr. Latin intensive prefix 're', and 'sentir' "to feel"). Ressentiment is a sense of hostility directed at that which one identifies as the cause of one's frustration, that is, an assignment of blame for one's frustration. The sense of weakness or inferiority and perhaps jealousy in the face of the "cause" generates a rejecting/justifying value system, or morality, which attacks or denies the perceived source of one's frustration. This value system is then used as a means of justifying one's own weaknesses by identifying the source of envy as objectively inferior, serving as a defense mechanism that prevents the resentful individual from addressing and overcoming their insecurities and flaws. The ego creates an enemy in order to insulate itself from culpability.
Max Scheler (1874–1928) was both the most respected and neglected of the major early 20th century German Continental philosophers in the phenomenological tradition. His observations and insights concerning "a special form of human hate" and related social and psychological phenomenon furnished a descriptive basis for his philosophical concept of "Ressentiment". As a widely recognized convention, the French spelling of this term has been retained in philosophical circles so as to preserve a broad sense of discursive meaning and application. Scheler died unexpectedly of a heart attack in 1928 leaving a vast body of unfinished works. Extrapolations from his thoughts have always since piqued interest and discussion on a variety of topics. His works were on the Nazi book burn list.
As a concept belonging to the study of ethics, Ressentiment represents the antithetical process of Scheler's emotively informed non-formal ethics of values. But Ressentiment can also be said to be, at once, Scheler's darkest as well as his most psychological and sociological of topics, foreshadowing many later findings in those particular social sciences.
Today we might associate Ressentiment with passive aggressive behavior: e.g., the power of labor unions to negotiate favorable work contracts through the use of strikes or production slow downs; or America's non-violent civil rights movement. But, folk wisdom comes closest to Scheler's meaning by recognizing Ressentiment as a self-defeating turn of mind which is non-productive and ultimately a waste of time and energy. Maturity informs most of us that sustained hatred hurts the hater far more than the object of our hate. Sustained hatred enslaves by preventing emotional growth from progressing beyond the sense of pain having been precipitated, in some way, by whom or what is hated (i.e., another person, group or class of persons).