rhetorical device

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A phrase (set phrase or created phrase) that uses reduplication, onomatopoeia, or other phonetic markers that increase memorability and “musicality” (making rhetoric pleasing or entertaining).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a use of language that creates a literary effect (but often without regard for literal significance)