The story
Blend of lap + napkin. Compare also Middle English lapkyn, lappekyn (“a piece of cloth worn over a helmet; lambrequin”), Middle Dutch lappekijn.
Etymology from Wiktionary, CC BY-SA 4.0.
lapkin
Today it means: A napkin for one's lap, often large, and typically used at outdoor food events (e.g. cookouts, camping, etc.). Full definition →