espionage vs undercover work

espionage and undercover work both are nouns.

Word	Noun	Adjective	Verb	Adverb
espionage	Yes	No	No	No
undercover work	Yes	No	No	No

As nouns, undercover work is a hypernym of espionage; that is, undercover work is a word with a broader meaning than espionage:

espionage: the systematic use of spies to get military or political secrets
undercover work: the act of keeping a secret watch for intelligence purposes

Other hypernyms of espionage include spying.

espionage (noun)	undercover work (noun)
the systematic use of spies to get military or political secrets	the act of keeping a secret watch for intelligence purposes