The Collaborative International Dictionary of English v.0.48:

Roommate \Room"mate`\, n.
   One of two or more occupying the same room or rooms; one who
   shares the occupancy of a room or rooms; a chum.
   [1913 Webster]

WordNet (r) 3.0 (2006):

roommate
    n 1: an associate who shares a room with you [syn: roommate,
         roomie, roomy]