Source : Webster's Revised Unabridged Dictionary (1913)

Blain \Blain\ (bl[=a]n), n. [OE. blein, bleyn, AS. bl[=e]gen;
   akin to Dan. blegn, D. blein; perh. fr. the same root as E.
   bladder. See {Bladder}.]
   1. An inflammatory swelling or sore; a bulla, pustule, or
      blister.

            Blotches and blains must all his flesh emboss.
                                                  --Milton.

   2. (Far.) A bladder growing on the root of the tongue of a
      horse, against the windpipe, and stopping the breath.

Source : WordNet®

blain
     n : an inflammatory swelling or sore