The word "decoy" entered English in the 1620s from Dutch de kooi, meaning "the cage." What makes this etymology remarkable is that English absorbed the Dutch definite article de along with the noun kooi, fusing them into a single English word. This process — borrowing a foreign article as part of a noun — is unusual but not unique: "alcohol" preserves the Arabic article al-, and "alchemy" does the same.
The Dutch kooi descended from Middle Dutch coie (cage), which came from Latin cavea (a hollow place, a cage, an enclosure). The same Latin word produced French cage, Italian gabbia, and Spanish jaula, as well as English "cave," "cavern," and "cavity." The connection between hollowness and enclosure is fundamental: a cage is a hollow space that confines, and a cave is a natural hollow that shelters.
The original eendenkooi (duck cage) was a sophisticated engineering structure that exploited duck behaviour. Built on the edges of ponds, these traps consisted of a curved, tapering channel called a pipe, covered with netting stretched over hoops. Tame ducks — the decoys in the modern sense — would swim into the entrance of the pipe, and wild ducks, naturally gregarious, would follow. As the pipe narrowed, a trained dog (the kooikerhondje, literally "cager's little dog") would appear at intervals, driving the ducks forward
Several eendenkooi structures survive and still operate in the Netherlands, some dating to the medieval period. The areas around them are kept exceptionally quiet — in Dutch law, eendenkooi enjoy special noise-protection status, and disturbing the peace near a duck decoy was historically punishable by fine.
The semantic expansion from a specific duck-trapping device to any lure or misleading device occurred rapidly in English. Military decoys — dummy tanks, false radio transmissions, inflatable aircraft — became a crucial element of warfare, particularly during World War II. Operation Bodyguard, the deception campaign supporting D-Day, deployed thousands of decoys to convince Germany that the invasion would target Calais rather than Normandy.
In modern usage, "decoy" has shed almost all connection to duck hunting. It serves as both noun and verb, applying to any situation where a false target diverts attention from a real one — from police decoy operations to phishing emails to basketball pump-fakes. The Dutch duck cage has become a universal metaphor for strategic misdirection.