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.
Proto-Indo-European root meaning "horn; head," with derivatives referring to horned animals, horn-shaped objects, and projecting parts.
It forms all or part of: alpenhorn; Capricorn; carat; carotid; carrot; carotene; cerato-; cerebellum; cerebral; cerebrum; cervical; cervix; charivari; cheer; chelicerae; corn (n.2) "hardening of the skin;" cornea; corner; cornet; cornucopia; cranium; flugelhorn; hart; hartebeest; horn; hornbeam; hornblende; hornet; keratin; kerato-; migraine; monoceros; reindeer; rhinoceros; saveloy; serval; triceratops; unicorn.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit srngam "horn;" Persian sar "head," Avestan sarah- "head;" Greek karnon "horn," koryne "club, mace," koryphe "head;" Latin cornu "horn," cervus "deer;" Old English horn "horn of an animal;" Welsh carw "deer."