Onesie comes from the word "one" and means a one-piece suit, usually in the form you use for lazy days at home. It is also used for one-piece snowsuits and one-piece motorcycle suits. The word is sometimes spelled onesy.
The name may be derived from the registered trademark Onesies®, which is a range of clothes for infant children. The word onesie (in singular) does however, in modern usage, more often mean a suit in adult size.
When I come home from work, I just like to change into my onesie and watch TV.
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