UK /ˌplɛn.ɪ.pəʊˈtɛn.ʃəɹ.i/ · US /plɛn.ɪ.poʊˈtɛn.ʃ(i)əɹ.i/
Etymology From Medieval Latin plēnipotentiārius (“having full power”), Late Latin plēnipotēns, from plēnus (“full”) + potēns (“mighty, powerful”).
1
A person invested with full powers, especially as the diplomatic agent of a sovereign state, (originally) charged with handling a certain matter.
None but the like-minded can come plenipotentiary to our court.1859, Henry David Thoreau, A Plea for Captain John Brown:
1937, P. G. Wodehouse, 'Lord Emsworth and Others', Overlook, Woodstock: 2002, p 232. Meeting him in the street and ignoring the foul bowler hat he wore on his walks abroad, you would have put him down as a Bishop in mufti or, at the least, a plenipotentiary at one of the better courts.
1 more example
Two of them are hanging up there on Golgotha, and that ought to be enough to show the authority of Rome’s ah plenipotentiary.1985, Anthony Burgess, Kingdom of the Wicked:
It was written of Henry George Ward, M.P. for Sheffield from 1837 to 1849, that "he was also much occupied with railway enterprise in the days of early speculation." This suggests a hard-bitten man of commerce, but Ward had served in the Diplomatic Service and he was Minister Plenipotentiary to Mexico before retiring in 1827 at the age of 30.1960 March 23, N. Caplan, “The Railway Member of Parliament”, in Railway Magazine, page 209: