Spy
2 of the 7 encyclopedias on this shelf carry an entry for Spy. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a secret emissary sent into the enemy's camp or territory to inspect their works, ascertain their strength and their intentions, to watch their movements, and report thereon to the proper officer. By the the laws of war among all civilized nations a spy is subjected to capital punishment. To be treated as a spy one must first be caught in the enemy's territory, and in dress other than the adopted military uniform of his country. It must also be clearly shown that the object of the accused person is to gain information for the enemy which it would be to their advantage to know. If, when captured, the prisoner can show that his errand in getting through was of a personal nature, or that he was trading with the enemy, he can only be In trying a held as a prisoner of war. spy his military rank counts for much. An officer of high rank receives a more thorough trial than a private, though both are tried by court-martial. In the United States the verdict is sent to the President or the Secretary of War or Navy, for approval before execution. When a spy is ca caught in the act all these formalities are omitted. He is tried by a drum-head court-martial; allowed to make an explanation and a verdict is rendered without much deliberation. If he is found guilty the verdict is sent to the highest commanding officer in camp, and on his approval is carried out, after which a full report is made to the President. The two most famous spies in American history are Nathan Hale and Maj. John Andre.
Aiton's Encyclopedia (1910)
in time of warfare, a secret messenger sent within the enemy's lines to gather information. A scout goes in his own uniform and, if taken, must be treated as a prisoner of war . The spy travels in disguise, trying to appear what he is not. Sometimes he borrows the uniform of the enemy and passes himself off under false pretenses. According to the laws of warfare the spy may be shot. Major Andre, it may be remembered, was taken within the American lines at Tarrytown, not wearing his own uniform and bearing dispatches from General Arnold to the British commander. Although claiming protection as a prisoner of war, he was shot by order of the military council and with the approval of General Washington. An officer may send out anyone under his command to scout, but may not require a subordinate to act as a spy. Nathan Hale, an American soldier, suffered a similar fate. See Andre ; Hale