To spy is to secretly watch someone. It’s not recommended unless you’re actually a spy, a person who is hired by a government or organization to keep tabs on enemies.

You might imagine a spy working for the CIA or the KGB, but there are also military spies who infiltrate their opponents' armies to get information, commit sabotage, or steal technology. Private businesses sometimes employ spies as well, to collect information about competitors. As a verb, to spy is to do what a spy does—or simply to see something: "I spy brownies on the kitchen counter!"

Definitions of spy

n (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors

undercover agent
Margarete Gertrud Zelle
Dutch dancer who was executed by the French as a German spy in World War I (1876-1917)
show 6 types...
hide 6 types...
counterspy, mole
a spy who works against enemy espionage
double agent
a spy who works for two mutually antagonistic countries
espionage agent
someone employed to spy on another country or business competitor
foreign agent
a spy for a foreign country
someone who takes up a position surreptitiously for the purpose of espionage
a spy or saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal
Type of:
intelligence agent, intelligence officer, operative, secret agent
a person secretly employed in espionage for a government

n a secret watcher; someone who secretly watches other people

“my spies tell me that you had a good time last night”
snoop, snooper
a spy who makes uninvited inquiries into the private affairs of others
shadow, shadower, tail
a spy employed to follow someone and report their movements
a secret listener to private conversations
Type of:
looker, spectator, viewer, watcher, witness
a close observer; someone who looks at something (such as an exhibition of some kind)

v watch, observe, or inquire secretly

sleuth, snoop, stag
Type of:
monitor, supervise
keep tabs on; keep an eye on; keep under surveillance

v catch sight of; to perceive with the eyes

show 7 types...
hide 7 types...
descry, espy, spot
catch sight of
detect, discover, find, notice, observe
discover or determine the existence, presence, or fact of
catch out, find out
trap; especially in an error or in a reprehensible act
detect some circumstance or entity automatically
find an instance of (a word or particular usage of a word)
discover traces of
observe as if with an eye
Type of:
comprehend, perceive
to become aware of through the senses

v catch sight of

descry, espy, spot
Type of:
catch sight of; to perceive with the eyes

v secretly collect sensitive or classified information; engage in espionage

spy for the Russians”
Type of:
enquire, inquire, investigate
conduct an inquiry or investigation of

Sign up, it's free!

Whether you're a student, an educator, or a lifelong learner, Vocabulary.com can put you on the path to systematic vocabulary improvement.