Elocutionary is the adjective that belongs to elocution. It means “about that careful, clear way of speaking in public” — the voice, the sounds, the control. An elocutionary exercise is a practice piece for the breath and the lips; elocutionary skill is that trained delivery. It is a rare, rather bookish word. Most people who need the idea will just say speech or elocution and leave this form to teachers and writers. It never means “good at speaking” by itself; it only points to that art.