The Collaborative International Dictionary of English v.0.48:

Madman \Mad"man\, n.; pl. Madmen.
   A man who is mad; lunatic; a crazy person.
   [1913 Webster]

         When a man mistakes his thoughts for person and things,
         he is mad. A madman is properly so defined.
                                                  --Coleridge.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Madmen
   ibid., a Moabite town threatened with the sword of the
   Babylonians (Jer. 48:2).