Green’s Dictionary of Slang

1. (orig. US) to improve one’s position, esp. by taking what one already has, material or otherwise, and using it as the basis of one’s next move.

[1828		Richmond (VA) Whig 20 Feb. 1/3: As well, sir, might you ask the adventurer at Faro, who paralees (I believe, sir, that most of us are old enough to remember the term, although I trust that with the practice it is quite obsolete) [DA]].
[1938		H. Asbury Sucker’s Progress 9: A gambler was given the privilege of ‘going paroli,’ a phrase which, incidentally, has been corrupted into parlay and is in common usage on the race tracks. In other words, a Faro player could parlay his winnings, if any, to a sum previously agreed upon as the extreme running limit, and then, if he wished, bet the whole upon a single card or combination].
1947		B. Schulberg Harder They Fall (1971) 27: A series of commodities which [...] could be parlayed into tidy fortunes.
1952		Lait & Mortimer USA Confidential 202: Doug Prince, who parlayed a gob of brown beef on a bun into a fortune as the Hamburger King of Houston.
1960		G. Swarthout Where the Boys Are 188: We had parlayed $50 each into a hemispheric total of $1500, net!
1999		E. Bunker Mr Blue 90: Don’t be parlayin’ nothin’ into somethin’.
2010		(con. 1973) C. Stella Johnny Porno 32: You gonna parlay the few bucks you have phoning bets in?

2. (US black) to calm down, to relax.

1997–2000		College Sl. Research Project (Cal. State Poly. Uni., Pomona) 🌐 Parlay (and) marinate (verb) To chill; to cool out; to relax.
2000		Ebonics Primer at www.dolemite.com 🌐 parlay Definition: to chill like a pimp mother fucker Example: Ray Ray, what’s yo’ ass doin’ today? Baby, I’m just parlayin!
2014		C. Eble (ed.) UNC-CH Campus Sl. Spring 2014.