What does "spying" mean?

espionage; the act of secretly gathering information

Spying

Common synonyms include: bugging, catching, cloak-and-dagger work, corporate spying, counterespionage, counterintelligence.

/ˈspaɪ.ɪŋ/ noun, verb

noun, verb ·Moderate ·College level

Noun

1
espionage; the act of secretly gathering information countable, uncountable
"There are two ways in which the obsessive character of jealousy tends to exert itself: one is in the need to know, the endless tests and investigations and spyings that are so characteristic of jealousy."
2
the act of detecting something; catching sight of something wordnet
3
the act of keeping a secret watch for intelligence purposes wordnet
4
keeping a secret or furtive watch wordnet

Verb

"She is an old hand at spying on tax evaders."

Etymology 1

From spy + -ing.

Etymology 2

Inherited from Middle English spyinge, spiyng, spyeng, equivalent to spy + -ing.