1.
private detective; private investigator
A person hired privately to investigate matters such as missing persons, cheating spouses, or corporate espionage.
2.
detective (in fiction)
A character who solves mysteries or crimes, especially in novels and media.
A 探偵 is a private investigator, not a police officer. Japanese detective agencies do a brisk trade in surveillance work — infidelity checks, background checks on a prospective spouse, tracing people who have gone missing — and clients hire (雇う) or commission (依頼する) them directly.
Formation: 探 'to search' + 偵 'to scout, to spy'.
Types
Collocations
A police detective is a 刑事 — a different job and a different word, though English uses 'detective' for both. In fiction the two are stock foils for each other, as in 名探偵コナン (Detective Conan).