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.
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            Bids his free soul expatiate in the skies. --Pope.
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   2. To enlarge in discourse or writing; to be copious in
      argument or discussion; to descant.
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            He expatiated on the inconveniences of trade.
                                                  --Addison.
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