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]