double up vs parlay

double up is not a noun while parlay is a noun.

Word	Noun	Adjective	Verb	Adverb
double up	No	No	Yes	No
parlay	Yes	No	Yes	No

As verbs, double up and parlay are synonyms defined as:

double up (noun)	parlay (noun)
	a series of wagers in which the winnings from one wager are used as a stake for the subsequent wagers

double up (verb)	parlay (verb)
stake winnings from one bet on a subsequent wager	stake winnings from one bet on a subsequent wager
bend over or curl up, usually with laughter or pain
share a room or a bed designed for only one person