noun A person who secretly watches and examines the actions of other individuals or organizations and gathers information on them (usually to gain an advantage).
noun A defensive player assigned to cover an offensive backfield player man-to-man when they are expected to engage in a running play, but the offensive player does not run with the ball immediately.
verb To act as a spy.
During the Cold War, Russia and America would each spy on each other for recon.
verb To spot; to catch sight of; to espy.
I think I can spy that hot guy coming over here.
verb To search narrowly; to scrutinize.
verb To explore; to see; to view; inspect and examine secretly, as a country.