Conversion (word formation)

In linguistics, conversion, also called zero derivation or null derivation, is a kind of word formation involving the creation of a word (of a new part of speech) from an existing word (of a different part of speech) without any change in form, which is to say, derivation using only zero. For example, the noun green in golf (referring to a putting-green) is derived ultimately from the adjective green.

Source: Wikipedia — Conversion (word formation) (CC BY-SA 4.0)