expatiate

verb3

1. •
   To write or speak at length; to be copious in argument or discussion.

   • [H]e expatiated on the inconveniences of trade, that carried from us the commodities of our country, and made a parcel of upstarts as rich as men of the most ancient families of England. — 1716
2. •
   (rare) To range at large, or without restraint.
3. •
   (no longer used) To expand; to spread; to extend; to diffuse; to broaden.