Merriam-Webster's Collegiate® Dictionary, 11th Edition
BRISTLE
I. noun
Etymology: Middle English bristil, from brust bristle, from Old English byrst; akin to Old High German burst bristle, and perhaps to Latin fastigium top
Date: 14th century
a short stiff coarse hair or filament, bristlelike adjective
II. verb (bristled; bristling)
Date: 15th century
transitive verb to furnish with bristles, to make bristly ; ruffle , intransitive verb
1. to rise and stand stiffly erect , to raise the bristles (as in anger), to take on an aggressively defensive attitude (as in response to a slight or criticism) ,
3. to be full of or covered with especially something suggestive of bristles , to be full of something specified