Spy, n.; pl. Spies.
Etymology: [See Spy, v., and cf. Espy, n.]
1. One who keeps a constant watch of the conduct of others. "These wretched spies of wit." Dryden.
2. (Mil.)
A person sent secretly into an enemy's camp, territory, or fortifications, to inspect his works, ascertain his strength, movements, or designs, and to communicate such intelligence to the proper officer. Spy money, money paid to a spy; the reward for private or secret intelligence regarding the enemy. -- Spy Wednesday (Eccl.), the Wednesday immediately preceding the festival of Easter; -- so called in allusion to the betrayal of Christ by Judas Iscariot.
Syn. -- See Emissary, and Scout.
2 other Webster entries under this spelling
Spy, v. t. [imp. & p. p. Spied; p. pr. & vb. n. Spying.]
To gain sight of; to discover at a distance, or in a state of concealment; to espy; to see. One in reading, skipped over all sentences where he spied a note of admiration. Swift.
2. To discover by close search or examination. Look about with yout eyes; spy what things are to be reformed in the church of England. Latimer.
3. To explore; to view; inspect; and examine secretly, as a country; -- usually with out. Moses sent to spy Jaazer, and they took the villages thereof. Num. xxi. 32.
Spy, v. i.
To search narrowly; to scrutinize. It is my nature's plague To spy into abuses. Shak.
Shades of meaning
The scout and the spy are both employed to obtain information of the numbers, movements, etc., of an enemy. The scout lurks on the outskirts of the hostile army with such concealment as the case admits of, but without disguise; a spy enters in disguise within the enemy's lines. A scout, if captured, has the rights of a prisoner of war; a spy is held to have forfeited all rights, and is liable, in case of capture, to capital punishment. An emissary is rather political than military; sent rather to secretly influence opponents than to bring information concerning them; so far as he does the latter, he is not only an emissary, but a spy.