spying

(noun) keeping a secret or furtive watch.

(noun) the act of keeping a secret watch for intelligence purposes. Synonyms: undercover work.

(noun) the act of detecting something; catching sight of something. Synonyms: detection, catching, espial, spotting.

(verb) catch sight of. Synonyms: descry, spot, espy, spy.

(verb) watch, observe, or inquire secretly. Synonyms: spy, stag, snoop, sleuth.

(verb) catch sight of; to perceive with the eyes. Synonyms: spy, sight. Example: "He caught sight of the king's men coming over the ridge."

(verb) secretly collect sensitive or classified information; engage in espionage. Synonyms: spy. Example: "Spy for the russians."