The Collaborative International Dictionary of English v.0.48:

Birrus \Bir"rus\, n. [LL., fr. L. birrus a kind of cloak. See
   Berretta.]
   A coarse kind of thick woolen cloth, worn by the poor in the
   Middle Ages; also, a woolen cap or hood worn over the
   shoulders or over the head.
   [1913 Webster]