The Collaborative International Dictionary of English v.0.48:

Bedfellow \Bed"fel`low\, n.
   One who lies with another in the same bed; a person who
   shares one's couch.
   [1913 Webster] Bedfere

WordNet (r) 3.0 (2006):

bedfellow
    n 1: a temporary associate; "politics makes strange bedfellows"
    2: a person with whom you share a bed

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "bedfellow":
   ace, adjunct, ally, amigo, associate, bedmate, bosom buddy,
   brother, brother-in-arms, buddy, bunkie, bunkmate, butty, camarade,
   chamberfellow, chum, classmate, coadjutor, cohort, colleague,
   comate, companion, company, compatriot, compeer, comrade,
   confederate, confrere, consociate, consort, copartner, crony,
   fellow, fellow member, fellow student, girl friend, gossip, mate,
   messmate, old crony, pal, pard, pardner, partner, playfellow,
   playmate, roommate, schoolfellow, schoolmate, shipmate,
   side partner, sidekick, teammate, workfellow, yokefellow,
   yokemate