Underground surrogate word for "okay". Stems from the 20s and 30s as a positive term for law enforcement agencies cracking down on organized crime and alcohol.
"Is that all fifty?"

-OR-

"Are you fifty?"

-OR-

"She's fifty."
by ZanzibarBreeze December 30, 2010
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Fifty caliber.. a round of ammunition the bullet of which is a half inch (12.7mm) in diameter.

A common .50 cal round is the .50 BMG (Browning Machine Gun), the round which is (unsurprisingly) designed for the Browning .50 caliber machine gun.

The BMG itself is the large belt-fed machine gun known as a Ma Deuce. It was invented at the time of WWII but has remained in manufacture to this day because it is a very sound and effective design which it would be kinda hard to really improve on.

Now however there are a lot of other guns, including shoulder-fired rifles and even a single-shot pistol, firing the BMG round.

Fifty can also refer to the weapon used to fire .50 caliber ammuntion.
The Huey door gunner grinned and opened up on the Viet geurillas with his fifty.
by Dirge October 6, 2004
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another name for mersh... or the weed one step above shwag... give you a shitty hi that only good if your just doing it to get stoned.
Colman and I bought that fifty at wallgreens from our usual.
by Dave-izzle September 28, 2005
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Fifty dollars worth of marijuana. (usually somewhere from 2 to 5 grams depending on the quality and dealer)
we went and bought a fifty and that sh*t lasted forever
by asfdg May 26, 2006
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Fifty is the cops. It comes from five O, which is from the tv show Hawaii Five O. So, five O makes fifty.
by Jimi Hoffa April 26, 2008
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