Green’s Dictionary of Slang

(US) abundantly, very much.

1831		W. Cobbett Cottage Economy B5: A leaden collar for the stick, with the hole in the collar plenty large enough .
1833		Sydney Morn. Herald 19 Sept. 6/2: White men all same brother; black man plenty corrobbery, plenty shake hands.
1885		Bulletin (Sydney) 20 June 6/1: Augustus turned to Roger Bede and patronisingly remarked, ‘Ah, Archbishop, you seem to have a very nice place here – plenty nice grass and some nice cows!’.
1897		A.H. Lewis Wolfville 110: You can gamble he’s got it plenty right.
1902		Bulletin (Sydney) 13 Dec. 14/3: Quite sure, father. Oh, I’m plenty strong enough to put a load of wood on the cart.
1915		D. Lowrie My Life out of Prison 78: The next time you start up a business without permission you’ll get yours, and get it good and plenty.
1925		D. Hammett ‘Corkscrew’ Story Omnibus (1966) 220: This thing in my hands would have mangled them plenty!
1935		J. Conroy World to Win 232: His home brew! Mama! What wallop! I drunk a quart, and believe me, good peoples, I felt it plenty.
1947		W.D. Overholser Buckaroo’s Code (1948) 60: This jigger [...] is a plenty tough hombre.
1952		J. Jones From Here to Eternity (1998) 632: The Malloy passed along a couple of tips that will help you plenty.
1961		R.A. Norton Through Beatnik Eyeballs 36: Got me no regular mates to speak of, nothing I plenty enjoys doing.
1971		T. Thackrey Thief 343: He was plenty calm.
1983		C. Heath A-Team 2 (1984) 33: We scared that mick plenty. I’ll think he’ll clam up.
1999		K. Sampson Powder 4: Plenty enough people had told Keva she liked him.
2001		N. Barlay Hooky Gear 130: Least looking round I’m in plenty company.