spy

transitive verb spied, spying

1. to watch or observe closely and secretly, usually with unfriendly purpose: often with out
2. to catch sight of; make out; perceive; see

intransitive verb

1. to watch or observe closely and secretly; specif., to act as a spy
2. to make a close examination or careful inspection

noun pl. spies

1. a person who keeps close and secret watch on another or others
2. ☆ a person employed by a government to get secret information about or monitor the affairs, plans, armed forces, etc. of another government
3. a person employed by a company, as in industry or commerce, to discover the business secrets of another company
4. Now Rare an act of spying

adjective

1. of or about spies or espionage
2. used for purposes of military espionage: spy plane, spy satellite