The /k/-sound was preserved by being redistributed to the preceding syllable: /əˈkn-/ > /əkˈn-/. The -c- was inserted accordingly to reflect this pronunciation more clearly.
[T]he charge of my moſt curious, and coſtly ingredients fraide, amounting to ſome ſeaventeene thouſand crovvnes, a trifle in reſpect of health, vvriting your noble name in my Catalogue, I ſhall acknovvledge my ſelfe amply ſatisfi'd.
1604, Jeremy Corderoy, A Short Dialogve, wherein is Proved, that No Man can be Saved without Good VVorkes, 2nd edition, Oxford: Printed by Ioseph Barnes, and are to be sold in Paules Church-yard at the signe of the Crowne, by Simon Waterson, →OCLC, page 40:
[N]ow ſuch a liue vngodly, vvithout a care of doing the wil of the Lord (though they profeſſe him in their mouths, yea though they beleeue and acknowledge all the Articles of the Creed, yea haue knowledge of the Scripturs) yet if they liue vngodly, they deny God, and therefore ſhal be denied, […]
Such an episode in the Island's grand naval story her naval historians naturally abridge; one of them (G.P.R. James) candidly acknowledging that fain would he pass it over did not "impartiality forbid fastidiousness."
1667, John Milton, “Book XI”, in Paradise Lost.[…], London: […] [Samuel Simmons], and are to be sold by Peter Parker[…]; [a]nd by Robert Boulter[…]; [a]nd Matthias Walker,[…], →OCLC; republished as Paradise Lost in Ten Books:[…], London: Basil Montagu Pickering[…], 1873, →OCLC:
They his gifts acknowledged none.
(transitive) To report (the receipt of a message to its sender).
This is to acknowledge your kind invitation to participate in the upcoming debate.
(transitive) To own as genuine or valid; to assent to (a legal instrument) to give it validity; to avow or admit in legal form.
1843, Thomas Isaac Wharton, A Digest of the Reported Cases Adjudged in the Several Courts Held in Pennsylvania, Together with Some Manuscript Cases:
One who has been sheriff may acknowledge a deed executed by him while in office.
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