1618, most likely from Du. kooi "cage," used of a pond surrounded by nets, into which wildfowl were lured for capture, from W.Gmc. *kaiwa, from L. cavea, "cage." The first element is possibly the Du. definite article de, mistaken in Eng. as part of the word. But decoy, of unknown origin, was the name of a card game popular c.1550-1650, and this may have influenced the form of the word.