The Collaborative International Dictionary of English v.0.48:

Chum \Chum\, n.
   Chopped pieces of fish used as bait. [U. S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chum \Chum\ (ch[u^]m), n. [Perh. a contraction fr. comrade or
   chamber fellow: cf. also AS. cuma a comer, guest.]
   A roommate, especially in a college or university; an old and
   intimate friend.
   [1913 Webster]

   New chum, a recent immigrant. [Australia]
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Chum \Chum\, v. i. [imp. p. p. Chummed; p. pr. & vb. n.
   Chumming.]
   To occupy a chamber with another; as, to chum together at
   college. [U. S.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

chum
    n 1: a close friend who accompanies his buddies in their
         activities [syn: buddy, brother, chum, crony,
         pal, sidekick]
    2: bait consisting of chopped fish and fish oils that are dumped
       overboard to attract fish
    3: a large Pacific salmon with small spots on its back; an
       important food fish [syn: chum salmon, chum,
       Oncorhynchus keta]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "chum":
   ace, amigo, associate, associate with, assort with, bedfellow,
   bedmate, bosom buddy, buddy, bunkie, bunkmate, butty, camarade,
   chamberfellow, chum together, chum with, classmate, clique,
   clique with, club together, colleague, comate, companion, company,
   compeer, comrade, confidante, confrere, consociate, consort,
   consort with, copartner, crony, familiar, fellow, fellow student,
   fellowship, flock together, fraternize, friend, girl friend,
   go with, gossip, hang around with, hang out with, herd together,
   hobnob with, join, join in fellowship, keep company with, mate,
   messmate, mingle with, mix with, old crony, pal, pal up with,
   pal with, pard, pardner, partner, playfellow, playmate, roommate,
   run in couples, run with, running mate, schoolfellow, schoolmate,
   shipmate, side partner, sidekick, sort with, take up with,
   team up with, teammate, tie up with, workfellow, yokefellow,
   yokemate