Since the 2000s, onesie // has become a commonly used word for a particular style of loose-fitting casual jumpsuits for adults made of knit cotton (as used in sweatshirts), fleece, or chenille. They are mostly intended as loungewear or sleepwear, but have gained significant popularity as stylish streetwear, especially in the UK and Australia, becoming increasingly popular during the late 2000s and early 2010s as a street fashion.
The term "onesies" (with an s at the end) is a brand name for infant bodysuits that is owned by Gerber Childrenswear LLC, and the term is used generically for infant bodysuits in the US. There is little in common between the infant onesies and an adult onesie: the former is usually sleeveless and legless and snaps or buttons at the crotch. In 2008, when casual jumpsuits became increasingly popular, the press started discrediting them as "adult onesies," and the name seems to have eroded to a generic word, dropping the final s in the process.
A type of onesie known as kigurumi (着ぐるみ), or "cosplay pajamas", emerged as Japanese street fashion and spread outside Japan in 2009 when they were exported by the Kigu company. Kigurumi can also refer to a costumed character, and these types of clothing resemble various types of animals, similar to a mascot costume. They became popular worldwide, in particular following a viral video of Miley Cyrus twerking while wearing a unicorn kigurumi.
- Siren suit – The 1940s precursor to the Onesie.
- Union suit – One-piece underwear invented during the mid-19th century and worn by cowboys and American Civil War soldiers.
- Blanket sleeper, an infant garment similar to an adult onesie
- "onesie | Definition of onesie in English by Oxford Dictionaries". Oxford Dictionaries | English. Retrieved 2018-07-09.
- Adult Onesies: The Dress Like A Toddler Trend Claims Further Victims. Archived 2012-10-14 at the Wayback Machine Blog entry in The Fashion Police dated 2008-09-08. Accessed 2013-03-09.
- "What's with all the animal onesies?". Daily Life. Retrieved 2018-12-26.