Originally: a butterfly or large moth. Later: specifically any of various swallowtail butterflies belonging to the large genus Papilio.
Valid publication as a genus name: Linnaeus in Systema Naturae (ed. 10, 1758) I. 458, after earlier use by him in Systema Naturae (1735), originally applied to all butterflies..
Origin
Mid 17th century; earliest use found in Philosophical Transactions of the Royal Society of London. From classical Latin pāpiliō butterfly, moth, of uncertain origin.