Origin

The character 偵 combines a person radical on the left (亻) with the component 貞 on the right, which serves as a sound hint for the pronunciation テイ. The left side indicates this character describes a type of person or human action, while the right component provides a rough phonetic guide. Over time, the character came to specifically denote someone who gathers information secretly—a spy—building on the general sense of "person" plus the sound pattern suggested by 貞.