expatiate

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.

To the pure mind of Isabella thought of no other had arisen; and it was far better that the generous romance of her young heart should expatiate on the rival in heaven, than for a moment dread a rival on earth, and therefore become subject to jealousy...

To range at large, or without restraint.

[L]ooks on heav'n with more than mortal eyes, / Bids his free ſoul expatiate in the skies, / Amidſt her kindred ſtars familiar roam, / Survey the region, and confeſs her home! Such was the life great Scipio once admir'd, / Thus Atticus, and Trumball thus retir'd.

To expand; to spread; to extend; to diffuse; to broaden.