Unconfirmed. Hypotheses include:
- Middle English grene horne, the horn of a newly slaughtered animal
- From the reference to an animal with green (that is, young) horns
- From 17th-century jewellery manufacturing, which used decorated horn impressed at a specific temperature. If heated too high (a common mistake by apprentices), the horn turned green.
- From a misappropriation of the German expression "grün hinter den Ohren" (to be green behind the ears).
greenhorn (plural greenhorns)
- (chiefly US) an inexperienced person; a novice, beginner or newcomer
1847, George Frederick Augustus Ruxton, Adventures in Mexico and the Rocky Mountains, page 267:
- The powers of the Canadian voyageurs and hunters in the consumption of meat strike the greenhorn with wonder and astonishment; and are only equalled by the gastronomical capabilities exhibited by Indian dogs, both following the same plan in their epicurean gorgings.
- See also Thesaurus:beginner