1. [n]  a stiff hair
2. [n]  a stiff fiber (coarse hair or filament); natural or synthetic
3. [v]  rise up; of animals fur or hair; as in fear; "The dog's fur bristled"; "It was a sight to make one's hair uprise!"
4. [v]  be in a state of movement or action; "The room abounded with screaming children"; "The garden bristled with toddlers"

BRISTLE is a 7 letter word that starts with B.

1. \Bris"tle\ (br[i^]s"s'l), n. [OE. bristel, brustel, AS.
   bristl, byrst; akin to D. borstel, OHG. burst, G. borste,
   Icel. burst, Sw. borst, and to Skr. bh[.r]shti edge, point,
   and prob, L. fastigium extremity, Gr. 'a`flaston stern of a
   ship, and E. brush, burr, perh. to brad. [root]96.]
   1. A short, stiff, coarse hair, as on the back of swine.
   
   2. (Bot.) A stiff, sharp, roundish hair. --Gray.
   
   

2. \Bris"tle\, v. t. [imp. & p. p. {Bristled}; p. pr. & vb.
   n. {Bristling}.]
   1. To erect the bristles of; to cause to stand up, as the
      bristles of an angry hog; -- sometimes with up.
   
            Now for the bare-picked bone of majesty Doth dogged
            war bristle his angry crest.          --Shak.
   
            Boy, bristle thy courage up.          --Shak.
   
   2. To fix a bristle to; as, to bristle a thread.
   
   

3. \Bris"tle\, v. i.
   1. To rise or stand erect, like bristles.
   
            His hair did bristle upon his head.   --Sir W.
                                                  Scott.
   
   2. To appear as if covered with bristles; to have standing,
      thick and erect, like bristles.
   
            The hill of La Haye Sainte bristling with ten
            thousand bayonets.                    --Thackeray.
   
            Ports bristling with thousands of masts. --Macaulay.
   
   3. To show defiance or indignation.
   
   {To bristle up}, to show anger or defiance.