Orotund:
marked by fullness, strength, and clarity of sound : sonorous [Merriam-Webster]
Seen in Thereby Hangs a Tale, by Charles Earle Funk:
Bill Robinson may have heard [“copacetic”] as a youngster; its orotund polysyllabism may have stuck in his mind, and, unconsciously, he may have appropriated it, perhaps ascribing to it a meaning of his own. [Section on “copacetic”.]
