onesie

American  

[wuhn-zee] / ˈwʌn zi /

noun

1. a one-piece leisure or sleeping garment for an adult, usually combining a long-sleeved top with long pants.

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Trademark.

1. Onesies, 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.

onesie British  

/ ˈwʌnzɪ /

noun

1. a one-piece garment combining a top with trousers, worn by adults as leisurewear

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Usage

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?[wuhn-zee]

Etymology

Origin of onesie

First recorded in 1980–85; originally a trademark

Example Sentences

As a parent, you wouldn’t want your child to be stuck forever wearing a onesie and drinking from a sippy cup.

From The Wall Street Journal • Jan. 1, 2026

The boy was last seen wearing a black onesie, authorities said.

From Los Angeles Times • Aug. 19, 2025

She had managed to consume 24 socks, a scrunchie, two hair ties, a shoe insert, a onesie and multiple pieces of cloth.

From Los Angeles Times • Feb. 26, 2025

Anna Parker found the image online: a teal onesie with a handwritten note pinned to the front.

From Seattle Times • Mar. 4, 2024

“Here comes the story,” I say, tapping the polka dots on the knees of her pajama onesie.

From "A High Five for Glenn Burke" by Phil Bildner