The Collaborative International Dictionary of English v.0.48:

Tweed \Tweed\, n. [Probably a corruption of twills. See
   Twill.]
   A soft and flexible fabric for men's wear, made wholly of
   wool except in some inferior kinds, the wool being dyed,
   usually in two colors, before weaving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tweed
    n 1: thick woolen fabric used for clothing; originated in
         Scotland
    2: (usually in the plural) trousers made of flannel or gabardine
       or tweed or white cloth [syn: flannel, gabardine,
       tweed, white]