The Collaborative International Dictionary of English v.0.48:

Congressional \Con*gres"sion*al\, a.
   Of or pertaining to a congress, especially, to the Congress
   of the United States; as, congressional debates.
   [1913 Webster]

         Congressional and official labor.        --E. Everett.
   [1913 Webster]

   Congressional District, one of the divisions into which a
      State is periodically divided (according to population),
      each of which is entitled to elect a Representative to the
      Congress of the United States.
      [1913 Webster]

WordNet (r) 3.0 (2006):

congressional
    adj 1: of or relating to congress; "congressional hearing"