1. giving out or capable of giving out a sound, esp. a deep, resonant sound, as a thing or place: a sonorous cavern. 2. loud, deep, or resonant, as a sound. 3. rich and full in sound, as language or verse. 4. high-flown; grandiloquent: a sonorous speech.

[1605–15; < L sonōrus noisy, sounding, equiv. to sonōr-, s. of sonor sound (son(āre) to SOUND1 + -or -OR1) + -us -OUS]

—so·norous·ly, adv.

—so·norous·ness, n.

—Syn.4. eloquent, florid, grandiose, orotund.

(Random House Webster's Unabridged)