cucumber (n.)
late 14c., from Old French cocombre (13c., Modern French concombre), from Latin cucumerem (nominative cucumis), perhaps from a pre-Italic Mediterranean language. The Latin word also is the source of Italian cocomero, Spanish cohombro, Portuguese cogombro. Replaced Old English eorþæppla (plural), literally "earth-apples."

Cowcumber was common form 17c.-18c., and that pronunciation lingered into 19c. Planted as a garden vegetable by 1609 by Jamestown colonists. Phrase cool as a cucumber (c.1732) embodies ancient folk knowledge confirmed by science in 1970: inside of a field cucumber on a warm day is 20 degrees cooler than the air temperature.