Expatiate

Verb

 * 1)  To range at large, or without restraint.
 * 2) To write or speak at length; to be copious in argument or discussion, to descant.
 * 3) * 2007: “It can't fly,” he expatiated. “It can move forward only by hopping.” — Clive James, Cultural Amnesia (Picador 2007, p. 847)
 * 4)  To expand; to spread; to extend; to diffuse; to broaden.

Thesaurus
amplify, descant, detail, develop, dilate, discuss, dissert, dissertate, elaborate, enlarge, enlarge upon, evolve, expand, explicate, narrate, particularize, ramble, recite, recount, rehearse, rehearse in extenso, relate, relate at large, sermonize, unfold, work out

Etymology
From the participle stem of Latin expatiari, from ex- + spatiari ‘walk about’.