Archaic term for a spy or undercover agent, sometimes associated with ninja in historical contexts. Not used in contemporary Japanese; modern equivalents include スパイ or 間諜 (かんちょう).
In the Warring States period, spies infiltrated enemy camps to gather intelligence.
Common modern word for 'ninja', while 細作 is an archaic synonym.
Borrowed from Chinese 細作, an established term for a spy or secret agent.