spy vs foreign agent

spy and foreign agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
spy	Yes	No	Yes	No
foreign agent	Yes	No	No	No

As nouns, foreign agent is a hyponym of spy; that is, foreign agent is a word with a more specific, narrower meaning than spy:

spy: (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors
foreign agent: a spy for a foreign country

Other hyponyms of spy include counterspy, mole, double agent, espionage agent, infiltrator, sleeper.

spy (noun)	foreign agent (noun)
(military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors	a spy for a foreign country
a secret watcher; someone who secretly watches other people

spy (verb)	foreign agent (verb)
secretly collect sensitive or classified information; engage in espionage
watch, observe, or inquire secretly
catch sight of
catch sight of; to perceive with the eyes