1. Plural of onesie; one-piece garments for infants or young children, typically with long sleeves and legs and snap or zipper closures.
Usage: informal; commonly used in North American English
2. Plural of onesie; one-piece pajamas or loungewear for older children or adults, often featuring a hood and animal or character designs.
Usage: informal; modern usage

Examples

• The baby wore colorful onesies during her first month of life.
• I packed several onesies for the newborn in the hospital bag.
• Teenagers often wear animal onesies as pajamas at sleepovers.
• The store sells onesies in various sizes, from newborn to adult.
• She bought matching onesies for her twins to make dressing easier.
• Onesies with snap buttons are convenient for quick diaper changes.