IPA: /ˈkaʊntərˌspaɪ/
KK: /ˈkaʊntərˌspaɪ/
A person who works to detect or counteract enemy spies and espionage activities.
The counterspy successfully uncovered the enemy's plans.
Counterspy → It is formed from "counter-" (meaning against) and "spy" (from Old French *espier*, meaning to observe secretly). The word "counterspy" refers to someone who observes or investigates against spies, often to thwart their activities.
Think of someone working 'against' ('counter-') those who 'observe secretly' ('spy') — that's what a counterspy does.
No commonly confused words.