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. [1913 Webster] Blotches and blains must all his flesh emboss. --Milton. [1913 Webster] 2. (Far.) A bladder growing on the root of the tongue of a horse, against the windpipe, and stopping the breath. [1913 Webster]