late 14c., piken "look quickly and slyly," a word of unknown origin. The words peek, keek, and peep all were used with more or less the same meaning 14c.-15c.; perhaps the ultimate source was Middle Dutch kieken. Related: Peeked; peeking.
"a peek, glance," 1844, from peek (v.).
I only peeked--I didn't see anything interesting