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; the onesie became very 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 the Gerber corporation, 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.
- 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.
- Kigurumi – Japanese suits which sometimes can have a similar look.
- 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. Blog entry in The Fashion Police dated 2008-09-08. Accessed 2013-03-09.