The Collaborative International Dictionary of English v.0.48:
Expatiate \Ex*pa"ti*ate\, v. i. [imp. & p. p. Expatiated; p.
pr. & vb. n. Expariating.] [L. expatiatus, exspatiatus, p.
p. of expatiari, exspatiari, to expatiate; ex out + spatiari
to walk about spread out, fr. spatium space. See Space.]
1. To range at large, or without restraint.
Bids his free soul expatiate in the skies. --Pope.
2. To enlarge in discourse or writing; to be copious in
argument or discussion; to descant.
He expatiated on the inconveniences of trade.