Green’s Dictionary of Slang

(US black) a large or infinite quantity.

1899		Sioux City Jrnl (IA) 2 Apr. 10/7: A man might have fifty eleven hobbies and unless she had one of them herself he could talk himself deaf, dumb and blind.
1919		Lincoln Jrnl Star (NE) 5 Aug. 12/2: He could live fifty-eleven years a benedict without ever thinking of it if left to his own devices.
1934		Battle Creek Enquirer (MI) 20 Apr. 8/4: Just about fifty eleven times more efficient than the old-fashioned wood frames.
1947		Indianapolis Star (IN) 1 June 16/7: ‘Back home we have fifty-eleven different flavors,’ GI Joe told her.
1965		News-Jrnl (Mansfield, OH) 28 May 20/6: ‘How old do you think Liston is now?’ Cassius was asked. ‘Fifty-eleven,’ he said.
1994		C. Major Juba to Jive 169: Fifty-eleven; fifty-’leven n. (1890s–1950s) a profuse or unaccountable quantity.
2005		W.D. Myers Autobiog. of My Dead Brother 118: I had promised myself fifty leben times I would stop drawing.