1520s, the older name of the nursery play known in U.S. as peek-a-boo; see peep (n.1).
also peek-a-boo, as the name of a children's game attested from 1590s; as an adjective (of garments) meaning "see-through, open," it dates from 1895. From peek (v.) + boo. Compare bo-peep.
updated on October 14, 2021