Source for all: etymonline.com
Assassin
A fanatical Ismaili Muslim sect of the mountains of Lebanon in the time of the Crusades, under leadership of the “Old Man of the Mountains”
Coward
mid-13c., from Old French coart “coward” from coe “tail,” from Latin coda, popular dialect variant of cauda “tail,”; The word probably reflects an animal metaphoric sense still found in expressions like turning tail and tail between legs.
Fanatic
1520s, “insane person,” from Latin fanaticus “mad, enthusiastic, inspired by a god,” also “furious, mad,” originally, “pertaining to a temple,”
Loser
mid-14c., “a destroyer” (a sense now obsolete), agent noun from lose (v.). Sense of “one who suffers loss” is from 1540s; meaning “horse that loses a race” is from 1902; “convicted criminal” is from 1912; “hapless person, one who habitually fails to win” is by 1955 in U.S. student slang. Bad loser (also poor, sore, etc.) “one who takes defeat with bad grace” is by 1892.
Nut
“crazy,” 1846, from earlier be nutts upon “be very fond of” (1785), which is possibly from nuts (plural noun) “any source of pleasure” (1610s), from nut (q.v.). Sense influenced probably by metaphoric application of nut to “head” (1846, as in to be off one’s nut “be insane,” 1860). Nuts as a derisive retort is attested from 1931.
Thug
1810, “member of a gang of murderers and robbers in India who strangled their victims,”
Zealot
early 14c., “member of a militant 1st century Jewish sect which fiercely resisted the Romans in Palestine,”