The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]