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]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "roommate":
   ace, amigo, associate, bedfellow, bedmate, birthmate, bosom buddy,
   buddy, bunkie, bunkmate, butty, camarade, chamberfellow, chum,
   classmate, clubmate, colleague, comate, companion, company,
   compeer, comrade, confrere, consociate, consort, copartner,
   copemate, copesmate, couchmate, cradlemate, crony, cupmate, fellow,
   fellow student, general partner, girl friend, gossip, jailmate,
   mate, messmate, old crony, pal, pard, pardner, partner, pewmate,
   playfellow, playmate, schoolfellow, schoolmate, secret partner,
   shelfmate, shipmate, shopmate, side partner, sidekick, sidekicker,
   silent partner, sleeping partner, special partner, tablemate,
   teammate, tentmate, watchmate, waymate, workfellow, yokefellow,
   yokemate