The word 'tush' presents a fascinating case of convergent evolution from different expressive origins. The noun for a pointed tooth, particularly a canine, derives from Old English tusc or tux, related to Old High German zusc, and is ultimately of Germanic origin, likely imitative of the action of drawing in breath or making a sharp sound. The interjection, used to express contempt or rebuke, is Middle English, natural exclamatory in origin. The humorous or archaic noun for the buttocks arose in the 20th century, likely as a euphemistic alteration of 'butt' influenced by the rounder, softer sound of 'tush'. These distinct streams of meaning coalesced into a single spelling, demonstrating how language can bundle unrelated expressive forms under one orthographic roof.

This word is a simplex. It is a native English word of imitative or expressive origin, not productively formed from separate morphemes.