spy
偵 centers on covert observation: a spy who secretly watches and gathers information.
偵 combines 亻 (person) with 貞, which likely contributes the sound and the idea of correctness or uprightness, suggesting a person who observes or investigates.
A person 亻 beside 貞, like a spy who stands upright and watches carefully, gathering information.
For テイ, imagine a spy taking a tea break while secretly watching: tea -> テイ.
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detective; investigator; sleuth
scouting; reconnaissance
secret investigation; private enquiry; private inquiry; reconnaissance; scouting
spy; secret agent
cybersleuth
reconnaissance plane; spy plane
reconnaissance satellite; spy satellite
player put on starting list to be replaced by another when the opponent's pitcher is known
scouting party; patrol
surveillance flight
spying out; discovering (by covert investigation)
great detective
Detective Conan (manga series and media franchise); Case Closed
reconnaissance in force; combat reconnaissance
armchair detective
detective bureau; detective agency; investigation firm
detective team
detective story
detective work; detective industry
detective agency