What is "migraine headache"

Megrim \Me"grim\, n. [OE. migrim, migrene, F. migraine, LL. hemigrania, L. hemicrania, hemicranium, Gr. ?; ?- half + ? skull. See Hemi- and Cranium, and cf. Hemicrania, Migraine.]

1. A kind of sick or nervous headache, usually periodical and confined to one side of the head; now more commonly called migraine headache or migraine.

2. A fancy; a whim; a freak; a humor; esp., in the plural, lowness of spirits.

   These are his megrims, firks, and melancholies.
   --Ford.

3. pl. (Far.) A sudden vertigo in a horse, succeeded sometimes by unconsciousness, produced by an excess of blood in the brain; a mild form of apoplexy.
   --Youatt.

migraine \mi*graine"\, n. [F. migraine, LL. hemigrania, L. hemicrania, hemicranium, Gr. "hmikrani`a; "hmi- half + krani`on skull. See Hemi- and Cranium, and cf. Hemicrania, Migraine.] 1. A kind of intense sick or nervous headache, usually periodical and confined to one side of the head; called also migraine headache. Same as megrim. -- Mi*grain"ous, a.

n. migraine.