the mind > attention and judgement > enquiry > investigation, inspection > secret observation, spying > [noun] > a secret observer, spy > a spy or scout (10)
Military. A person employed in time of war to obtain secret information regarding the enemy; in early use esp. one venturing in disguise into the…
One who espies or spies out; †a spy.
concrete. A body of spies; hence (chiefly in plural) a spy, scout. Obsolete.
slang. A college servant who is inclined to pass on information to someone in authority; a telltale. Obsolete. rare.