THESAURUS
spying
bugging, cloak-and-dagger work, counterespionage, counterintelligence, detection, electronic surveillance, espial, espionage, following, intelligence, intelligence work, looking, lookout, military intelligence, note, notice, observance, observation, regard, respect, secret police, secret service, shadowing, stakeout, surveillance, tailing, trailing, viewing, watch, watching, wiretap, wiretapping, witnessing