Green’s Dictionary of Slang

1. a know-it-all, a self-appointed smart fellow.

1902		Ade Girl Proposition 72: The Original Gentleman Friend was a Wisenstein. As soon as he saw himself losing out, he began to lay deep and shifty Plans.
1922		S. Lewis Babbitt (1974) 228: The wisenheimers grab a look at a fellow’s nails when they want to tell if he’s a tinhorn or a real gent!
1938		W. Winchell On Broadway 23 Nov. [synd. col.] The wisenheimer laughed and took the wager.
1947		B. Schulberg Harder They Fall (1971) 208: He ain’t quite the weisenheimer he was when he came in from Two.
1957		J.D. Salinger in Rawson Wicked Words (1989) 420: We were nervous [...] at the statistics on child pedants and academic wisenheimers who grow up into faculty-recreation-room savants .
1962		R. Dougherty Commissioner 44: These two wisenheimers wound up getting treated like hicks in a whorehouse.
1975		L. Rosten Dear ‘Herm’ 100: In case some wisenheimer in our midst throws Mr. Pulsifer [...] a slider.
1982		S. King Different Seasons (1995) 486: The cabbie gave a why-do-I-always-get-the-wisenheimers snort ... but he shut up.
1991		(con. 1920s) O.D. Brooks Legs 53: I was certain some wisenheimer had learned about our intended break and ratted.
2002		J. Meades Fowler Family Business 84: Sullen Ben and the Wisenheimer Lennie.
2016		T. Robinson Rough Trade [ebook] ‘Night, Bagger Vance.’ ‘Wisenheimer’.

2. attrib. use of sense 1.

1929

D. Hammett ‘Fly Paper’ Story Omnibus (1966) 52: He smiled that wisenheimer smile of his.