noun

(grammar, narrow sense) A word that can be used to refer to a person, animal, place, thing, phenomenon, substance, quality, or idea; one of the basic parts of speech in many languages, including English.

(grammar, now rare, broad sense) Either a word that can be used to refer to a person, animal, place, thing, phenomenon, substance, quality or idea, or a word that modifies or describes a previous word or its referent; a substantive or adjective, sometimes also including other parts of speech such as numeral or pronoun.

To convert a word to a noun.