Onesie comes from the word "one" and means a one-piece suit, usually in the form you use for lazy days at home. It is also used for one-piece snowsuits and one-piece motorcycle suits. The word is sometimes spelled onesy.

The name may be derived from the registered trademark Onesies®, which is a range of clothes for infant children. The word onesie (in singular) does however, in modern usage, more often mean a suit in adult size.
When I come home from work, I just like to change into my onesie and watch TV.
by EliasG June 4, 2013
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sexyyy !
sexiest garment on earth ;)
ninette: yo bry, r u going to the pajama party ?
bry: yea im wearing my onesies
ninnete: sexayyy ! ;)
by cytb March 27, 2011
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One piece long underwear, generally worn by infants and toddlers. Plural of onesie.
I have a drawer full of onesies from when I was five years old.
by phreek123 October 20, 2008
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A one piece snow suit. Worn back in the day when skiing was young. Now commonly worn by thy Gaper. Comes in Solid or Multiple bright colors. Do NOT wear in Colorado or you shall get mugged.
For Gaper day, I decided to wear a Onesy.
by A Local Coloradian May 3, 2009
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A beautiful, intelligent young women.
guy: hey have you seen onesis?
guy #2: yea, she is beautiful...
by 1234blahblahblah1234 January 31, 2011
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Warm terry-cloth awesomeness shaped like different characters.
"If your onesie doesnt have a butt flap, you're gonna have a two-sie"
by ElizabethDrake May 8, 2018
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N. urination. Derived from the term number one. Originally used in the sitcom show Scrubs.
"Sorry, gotta go make onesies."
by Scrubby May 6, 2008
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