The Collaborative International Dictionary of English v.0.48:

Scaldfish \Scald"fish`\, n. [Scald, a. + fish.] (Zool.)
   A European flounder (Arnoglossus laterna, or Psetta
   arnoglossa); -- called also megrim, and smooth sole.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Megrim \Me"grim\, n. [Etymol. uncertain.] (Zool.)
   The British smooth sole, or scaldfish (Psetta arnoglossa).
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster +PJC]

   2. A fancy; a whim; a freak; a humor; esp., in the plural,
      lowness of spirits.
      [1913 Webster]

            These are his megrims, firks, and melancholies.
                                                  --Ford.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

megrim
    n 1: a severe recurring vascular headache; occurs more
         frequently in women than men [syn: migraine, megrim,
         sick headache, hemicrania]