spy

A person who secretly watches and examines the actions of other individuals or organizations and gathers information on them (usually to gain an advantage).

To act as a spy.

“During the Cold War, Russia and America would each spy on each other for recon.”

To spot; to catch sight of.

“I think I can spy that hot guy coming over here.”

To search narrowly; to scrutinize.

To explore; to see; to view; inspect and examine secretly, as a country.