The story
All senses from diaper + liner (“a removable cover or lining”).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A removable stay-dry (“permeable; referring to a material that allows liquid to wick through”) cover placed inside of a cloth diaper that catches solids while allowing the urine to wick through to the diaper's absorbent layers below, intended to make washing cloth diapers easier. Full definition →
All senses from diaper + liner (“a removable cover or lining”).
Etymology from Wiktionary, CC BY-SA 4.0.