: to spend time with someone as a friend—usually used with around
In the early '50s he entered Cornell University but quit after two years and lit out for Greenwich Village, where he studied drama and chummed around with James Dean. William Plummer et al.
Note: The word is apparently first attested along the New England coast. The Dictionary of American Regional English suggests a relation to "obs[olete] Engl[ish] & Scots dial[ect] chum food," but the sole attestation of such a word ("chum food, provision for the belly, Clydes[dale]") is in John Jamieson's Etymological Dictionary of the Scottish Language (1808). Possibly related is chum "a formless mass (of vegetables) from over-boiling," in the Dictionary of Newfoundland English, which points to Ulster Scots champ "potatoes, boiled and mashed," recorded in Joseph Wright's English Dialect Dictionary. This would presumably connect the word to champ entry 1.