O.E. byrst "bristle," with metathesis of -r-, from P.Gmc. *bors- (cf. M.Du. borstel, Ger. borste), from PIE *bhrsti- from base *bhar- "point, bristle" (cf. Skt. bhrstih "point, spike"). With -el, dim. suffix. The verb "become angry or excited" is 1540s, from the way animals show fight. Related: Bristled; bristling.