mid-15c., "box, case," from Old French tronc "alms box in a church," also "trunk of a tree, trunk of the human body, wooden block" (12c.), from Latin truncus "trunk of a tree, trunk of the body," of uncertain origin, perhaps originally "mutilated, cut off." The meaning "box, case" is likely to be from the notion of the body as the "case" of the organs. English acquired the "main stem of a tree" and "torso of the body" senses from Old French in late 15c. The sense of "luggage compartment of a motor vehicle" is from 1930. Railroad trunk line is attested from 1843; telephone version is from 1889.

"elephant's snout," 1560s, apparently from trunk, n.1, perhaps from confusion with trump, n.2, short for trumpet.