'greenhorn' originates from English (early 17th century), formed from 'green' meaning 'fresh' or 'new' and 'horn' referring literally to the horn of a young animal; together used figuratively for an unseasoned or inexperienced person.

'greenhorn' appeared in Early Modern English as a compound (often written 'green-horn' or 'greenhorn') and was used in the 17th century to describe callow youth or newcomers; it has remained largely unchanged into modern English, with the plural 'greenhorns' used for multiple inexperienced people.

Initially it referred literally to young animals with 'green' (fresh) horns and then figuratively to inexperienced persons; over time the meaning stabilized as 'novice' or 'inexperienced person.'