Plenty
Middle English (in the sense ‘fullness, perfection’): from Old French plente, from Latin plenitas, from plenus ‘full’.
wiktionary
From Middle English plentie, plentee, plente, from Anglo-Norman plenté, from Old French plenté, from Latin plenitatem, accusative of plenitas(“fullness”), from plenus(“complete, full”), from Proto-Indo-European *pl̥h₁nós(“full”), from which English full also comes, via Proto-Germanic. Related to the Latin derivatives complete, deplete, replete.
etymonline
plenty (n.)
mid-13c., "abundance; as much as one could desire; an ample supply," from Old French plentee, earlier plentet "abundance, profusion" (12c., Modern French dialectal plenté), from Latin plenitatem (nominative plenitas) "fullness," from plenus "full, filled, greatly crowded; stout, pregnant; abundant, abounding; complete," from PIE root *pele- (1) "to fill."
From early 14c. as "a large amount, a great deal." The meaning "condition of general abundance" is from late 14c. The colloquial adverb meaning "very much" is first attested 1842. Middle English had parallel formation plenteth, from the older Old French form of the word.
