late 14c., migrane, "severe headache, especially on one side of the head," from Old French migraine, migraigne (13c.), from the vulgar pronunciation of Late Latin hemicrania "pain in one side of the head, headache," from Greek hēmikrania, from hēmi- "half" + kranion "skull" (see cranium).
The corrupt form megrim was common from 15c. on and is the principle entry for the word in Century Dictionary (1895), but it seems to be now obsolete or archaic even in its secondary senses of "depression; low spirits" and "a whim or fancy." Related: Migrainous.
the worm or grub of various insects (especially a fly), formerly supposed to be generated by corruption, late 15c., magat, probably an unexplained variant of Middle English maddok, maðek "earthworm, bedbug, maggot," from Old English maða "maggot, grub," from Proto-Germanic *mathon (source also of Old Norse maðkr, Old Saxon matho, Middle Dutch, Dutch made, Old High German mado, German Made, Gothic maþa "maggot").
Figurative use "whim, fancy, crotchet" is 1620s, from the notion of a maggot in the brain. Hence maggotry "folly, absurdity" (1706).
1670s, "knot-like contraction or short twist in a rope, thread, hair, etc., originally a nautical term, from Dutch kink "twist in a rope" (also found in French and Swedish), which is probably related to Old Norse kikna "to bend backwards, sink at the knees" as if under a burden" (see kick (v.)). Figurative sense of "odd notion, mental twist, whim" first recorded in American English, 1803, in writings of Thomas Jefferson; specifically "a sexual perversion, fetish, paraphilia" is by 1973 (by 1965 as "sexually abnormal person").
1590s, an abusive term for a person, perhaps meaning "a pedant;" c. 1600, "a whim;" 1640s, "pun or word-play," a word of unknown origin, said in 17c. to be Oxford University slang. Perhaps the sort of ponderous mock-Latin word that was once the height of humor in learned circles; Skeat suggests Latin conandrum "a thing to be attempted" as the source. Also spelled quonundrum.
From 1745 as "a riddle in which some odd resemblance is proposed between things quite unlike, the answer often involving a pun." (An example from 1745: "Why is a Sash-Window like a Woman in Labour? because 'tis full of Panes").
late 14c., nocioun, "a general concept, conception," from Latin notionem (nominative notio) "concept, conception, idea, notice," noun of action from past participle stem of noscere "come to know," from PIE root *gno- "to know." Coined by Cicero as a loan-translation of Greek ennoia "act of thinking, notion, conception," or prolepsis "previous notion, previous conception."
Meaning "an opinion, a view, a somewhat vague belief" is from c. 1600; that of "a not very rational inclination, a whim" is by 1746. Notions in the concrete sense of "miscellaneous small articles of convenience or utensils" (such as sold by Yankee peddlers) is by 1803, American English, via the idea of "clever product of invention."