[ wuhn-zee ]
/ ˈwʌn zi /
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a one-piece leisure or sleeping garment for an adult, usually combining a long-sleeved top with long pants.
Onesies, Trademark. a brand name for one-piece garments for infants, the lower portion resembling briefs and having snaps across the crotch for convenience in diapering. Although a trademarked term, it is often spelled as lowercase onesie, referring to a single garment.
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Origin of onesie

First recorded in 1980–85; originally a trademark
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What else does onesie mean?

A onesie is a one-piece item of loungewear or sleepwear. Traditionally, onesies are worn by babies, but they exploded into adult novelty fashion in the 2010s.

How is onesie pronounced?


Where does onesie come from?

The cozy onesie has its fashion origins where the people needed it most: chilly, rainy, 1940s Great Britain. Winston Churchill is said to have designed the first one (complete with pinstripes) because it was warm and easy to wear over his pajamas in night raids during WWII. He even wore it to a meeting with General Dwight Eisenhower.

The Brits seemed to like the new clothing item, though. Londoners made the onesie their own and even started dressing their babies in onesies in the 1950s after they had fallen out of adult fashion.

In the early days, onesies were known as siren suits or union suits. It was with U.S. baby fashion in the early 2000s that the term onesie really started to spread, though the word dates back to the 1980s (a one-piece garment with the cutesy –sy/ or -sie suffix). Fun fact? Previous, unrelated meanings of onesie include a move in the game of jacks. Also, just so you know, onesie is technically a trademarked term by Gerber, so don’t go selling your homemade onesies by that name.

By the 2010s, adults had taken the onesie back. Google searches for onesie peak reliably every year around Halloween and Christmas as consumers online shop for costumes and excuses for a terrible Christmas morning onesie photo op.

How is onesie used in real life?

Today, onesie conversation is split between baby and adult fashion. Baby onesies usually snap at the crotch and have sleeves but not legs. Adult onesies tend to be one-piece pajama tops and bottoms.

When discussing the tiniest onesies for children, you’re most likely to see discussions of the best fabrics for the baby’s sensitive skin. You’ll also probably run into some funny (and often tasteless) sayings printed on baby onesies.

Adult onesies are pushed by lifestyle writers and wearers alike as cozy, warm, and soft. They’re a go-to for a lazy day.

Adult onesies aren’t just about the comfort. They’re also often seen as silly, especially those designed to look like giant animals. It’s not uncommon to see fans freak out over seeing their favorite celebrities in onesies.


Onesies are also pretty popular in what’s known as the “adult baby” fetish community.

More examples of onesie:

“Witty, wry, and even cloying sayings are trending in children’s clothing. On shelves now at Old Navy are onesies declaring “The snuggle is real” and “You had me at milk.” Crazy 8, a division of Gymboree Corp., sells “Smart like Mommy” and “I try to behave” T-shirts.”
Elizabeth Holmes, The Wall Street Journal, November, 2016


This content is not meant to be a formal definition of this term. Rather, it is an informal summary that seeks to provide supplemental information and context important to know or keep in mind about the term’s history, meaning, and usage.

How to use onesie in a sentence

British Dictionary definitions for onesie

/ (ˈwʌnzɪ) /

a one-piece garment combining a top with trousers, worn by adults as leisurewear
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012