Nappy and diaper refer to the same absorbent garment worn by babies; which one you use comes down to dialect. British English says nappy, American English says diaper. A useful hook: nappy is short, built on napkin, while diaper is the older word that American English kept and British English largely dropped in this sense.
The core difference
Nappy and diaper name the same baby garment; nappy is the British term and diaper is the American one.
- nappy — the British word for an absorbent garment worn by babies: Could you grab a clean nappy from the bag?
- diaper — the American word for the same garment: She changed the baby's diaper before putting him down for a nap.
- diaper — also a woven fabric with a small repeating diamond pattern: The tablecloth was made of fine linen diaper.
How to tell them apart
The garment is identical, so the choice is purely about audience. British writing, packaging and parenting sites say nappy; American ones say diaper. Because so much parenting content online is American, diaper turns up constantly even in British contexts, but nappy remains the word British parents actually use day to day.
Nappy has one other sense worth knowing: as an adjective it can describe tightly curled or frizzy hair, most often Afro-textured hair, a meaning that has nothing to do with the baby garment. Diaper also branches off on its own, naming a small diamond-patterned woven fabric, a much older use of the word than the baby item.
