A trademark registered to Gerber Childrenswear LLC, often used in connection with a one-piece garment for an infant or small child, generally worn over a diaper.

When a girl is so tight, you can only fit one finger in her.

a single cigarette sold over the counter by a retail establishment, instead of a pack of 20. useful in New York if you don't have the $8 for a pack. also useful for the quitting smoker who just needs one nicotine hit to take the edge off. onesie's are illegal in some states - eg Illinois 2009

A self rolled spliff that is the size of a rollie cigarette, using one regular sized rolling paper/skin.

to masturbate, have sex with oneself, to commit onanism