To look slyly, or with the eyes half closed, or through a crevice; to peep.
To be only slightly, partially visible, as if peering out from a hiding place.
A quick glance or look.
To be devious and cunning so as not to be seen.
To secretly spy on or investigate, especially into the private personal life of others.
The act of snooping
A private detective
One who snoops