Carpenter: “the art of telling some one else in words exactly what you mean to say” (Exercises in Rhetoric and English Composition, 1).
This definition includes both composition and orality, despite the inclusion of “to say” with its implicit speech. That is a plus.
On the minus side, words limit rhetoric. It precludes visual culture as rhetoric. It precludes events and art installations as rhetorical.
This definition, I think, is far too limiting for my understanding of rhetoric today, though it might be useful as a working definition for a beginning writer.