See noun in Webster's New World College Dictionary
noun
Gram. any of a class of words naming or denoting a person, thing, place, action, quality, etc. (Ex.: woman, water, New York, talking, beauty)
See noun in American Heritage Dictionary 4
(noun)
noun Abbr. n.
The part of speech that is used to name a person, place, thing, quality, or action and can function as the subject or object of a verb, the object of a preposition, or an appositive.
Any of the words belonging to this part of speech, such as neighbor, window, happiness, or negotiation.