Chum, n.
Etymology: [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.
2 other Webster entries under this spelling
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.]
Chum, n.
Chopped pieces of fish used as bait. [U. S.]
Shades of meaning
Fernald has no entry of its own for chum; he lists it under associate.
He lists it without comment; the entries above explain its neighbors.