n. pl. spies (spīz)
1. One who secretly collects information concerning the enemies of a government or group.
2. One who secretly collects information for a business about one or more of its competitors.
3. One who secretly keeps watch on another or others.
v. spied (spīd), spy·ing, spies (spīz)
1. To watch or observe secretly: was sent to spy out the enemy camp.
2. To discover by close observation: "[They] are continually prowling about on all three decks, eager to spy out iniquities" (Herman Melville).
3. To catch sight of; see: spied the ship on the horizon.
1. To engage in espionage.
2. To investigate or observe something, especially in secret: spying into the neighbor's activities.
[Middle English spie, from Old French espie, from espier, to watch, of Germanic origin; see spek- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.