The Collaborative International Dictionary of English v.0.48:

Congressman \Con"gress*man\, n.; pl. Congressmen.
   A member of the Congress of the United States, esp. of the
   House of Representatives.
   [1913 Webster]

WordNet (r) 3.0 (2006):

congressman
    n 1: a member of the United States House of Representatives
         [syn: congressman, congresswoman, representative]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "congressman":
   MP, Member of Congress, Member of Parliament, alderman,
   assemblyman, chosen freeholder, city father, congresswoman,
   councilman, floor leader, lawgiver, lawmaker, legislator,
   majority leader, minority leader, party whip, representative,
   senator, solon, state senator, whip