The Collaborative International Dictionary of English v.0.48:

Committeeman \Com*mit"tee*man\, n.
   A member of a committee.
   [1913 Webster]

WordNet (r) 3.0 (2006):

committeeman
    n 1: a man who is a member of committee

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "committeeman":
   Greek, affiliate, associate, belonger, brother, card-carrier,
   card-carrying member, cardholder, charter member, clubber, clubman,
   clubwoman, committeewoman, comrade, conventioneer, conventioner,
   conventionist, district leader, dues-paying member, enlistee,
   enrollee, fellow, fraternity man, guildsman, honorary member,
   initiate, insider, joiner, life member, member, national chairman,
   one of us, party chairman, pledge, political worker,
   precinct captain, precinct leader, sister, socius, sorority girl,
   sorority woman, state chairman