c. 1400, "to loathe, regard with repugnance, dislike intensely," literally "to shrink back with horror or dread," from Latin abhorrere "shrink back from, have an aversion for, shudder at," from ab "off, away from" (see ab-) + horrere "tremble at, shudder," literally "to bristle, be shaggy," from PIE *ghers- "start out, stand out, rise to a point, bristle" (see horror).
Formerly also "fill (someone) with horror or loathing" (16c.). In Latin it was less intense: "be remote from, vary from, differ from, be out of harmony with." Related: Abhorred; abhorring.
In England, the usual name is rocket (see rocket (n.1)), which is from Italian ruchetta via French roquette. It also sometimes is called hedge mustard.
Old English hær "hair, a hair," from Proto-Germanic *hēran (source also of Old Saxon, Old Norse, Old High German har, Old Frisian her, Dutch and German haar "hair"), perhaps from PIE *ghers- "to stand out, to bristle, rise to a point" (source also of Lithuanian šerys "bristle;" see horror).
Spelling influenced by Old Norse har and Old English haire "haircloth," from Old French haire, from Frankish *harja or some other Germanic source (see above). Hair-dye is from 1803. To let one's hair down "become familiar" is first recorded 1850. Homeopathic phrase hair of the dog (that bit you), remedy from the same thing that caused the malady, especially a drink on the morning after a debauch, 1540s in English, is in Pliny.
Still used for "hedgehog" in non-standard speech in Cumbria, Yorkshire, Shropshire. Applied throughout 16c. to people whose appearance or behavior suggested hedgehogs, from hunchbacks (1520s) to goblins (1580s) to bad girls (1530s); meaning "poorly or raggedly clothed youngster" emerged 1550s, but was not in frequent use until after c. 1780. Sea urchin is recorded from 1590s (a 19c. Newfoundland name for them was whore's eggs); Johnson describes it as "a kind of crabfish that has prickles instead of feet."
Canaanite god frequently mentioned in Scripture, said to have been propitiated by sacrificing children (Leviticus xviii.21), from Latin Moloch, from Greek Molokh, from Hebrew molekh, from melekh "king," altered by the Jews with the vowel points from basheth "shame" to express their horror of the worship. Hence, figuratively, "any baleful influence to which everything is sacrificed" (1799).
"become tiresome or insipid," 1700, a surviving transferred or figurative sense from the earlier meaning "become faint, fail in strength," from Middle English pallen (late 14c.), which is apparently [OED] a shortened form of appallen "to dismay, fill with horror or disgust" (see appall). Related: Palled; palling.
