> chum /tʃʌm/, sb.1 Now colloq.
Also 8 chumm.
Etymology: Recorded only since c 1684. A well-known conjecture is that it was a familiar abbreviation of chamber-fellow, chamber-mate, or the like. But no historical proof or connecting link has been found.
1. a. One who shares apartments with another or others, one who lodges or resides in the same room or rooms: ‘a chamber-fellow, a term used in the universities’ (J.); also, more generally, a habitual companion, an associate, an intimate friend. Now chiefly in familiar colloquial use with school-boys, fellow-students; also with criminals, co…