From the participle stem of Latin expatior, from ex- + spatior ("walk about").

• IPA: /ɪkˈspeɪʃɪeɪt/, /ɛkˈspeɪʃɪeɪt/

expatiate (expatiates, present participle expatiating; simple past and past participle expatiated)

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

   Synonyms: descant, dilate, enlarge, expound

   • 1716 March 16 (Gregorian calendar), Joseph Addison, “The Free-holder: No. 22. Monday, March 5. [1716.]”, in The Works of the Right Honourable Joseph Addison, Esq; […], volume IV, London: […] Jacob Tonson, […], published 1721, →OCLC ↗, page 438 ↗:

     [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.

   • 1842, [anonymous collaborator of Letitia Elizabeth Landon], “(please specify the page)”, in Lady Anne Granard; or, Keeping up Appearances. […], volume II, London: Henry Colburn, […], →OCLC ↗, pages 48–49 ↗:

     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...

   • 1851 November 13, Herman Melville, “The Mast-head”, in Moby-Dick; or, The Whale, 1st American edition, New York, N.Y.: Harper & Brothers; London: Richard Bentley, →OCLC ↗, page 203 ↗:

     Now, as the business of standing mast-heads, ashore or afloat, is a very ancient and interesting one, let us in some measure expatiate here.

2. (rare) To range at large, or without restraint.
   • 1713, Alexander Pope, “Windsor-Forest. […]”, in The Works of Mr. Alexander Pope, volume I, London: […] W[illiam] Bowyer, for Bernard Lintot, […], published 1717, →OCLC ↗, page 62 ↗:

     [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.

3. (obsolete) To expand; to spread; to extend; to diffuse; to broaden.

• French: parler longuement, appesentir sur quelque chose
• Russian: распространя́ться