He had told her all he had been asked to tell--or all he meant to tell: at any rate he had been given abundant opportunity to expatiate upon a young man's darling subject--himself.
-- Henry Blake Fuller, Bertram Cope's Year
At the midday meal on fair day, a large one (meat loaf, boiled potato, broccoli), Mrs. Lucas, married to the man with the earache, expatiates on the difficulties of caring for a parakeet her daughter has unloaded upon her and which, let out of its cage for an airing, has escaped through the door suddenly opened by Mr. Lucas.
-- William H. Pritchard, Updike: America's Man of Letters
His relationship with his family was for many years an unhappy one, and he does not care to expatiate upon it.
-- Barbara La Fontaine, "Triple Threat On, Off And Off-Off Broadway", New York Times, February 25, 1968
Expatiate is from Latin expatiari, "to walk or go far and wide," from ex-, "out" + spatiari, "to walk about," from spatium, "space; an open space, a place for walking in."