Definition

A noun is the name of a person, place, thing, or idea. Whatever exists, we assume, can be named, and that name is a noun. A proper noun, which names a specific person, place, or thing (Carlos, Queen Marguerite, Middle East, Jerusalem, Malaysia, Presbyterianism, God, Spanish, Buddhism, the Republican Party), is almost always capitalized. A proper noun used as an addressed person's name is called a noun of address. Common nouns name everything else, things that usually are not capitalized.

A group of related words can act as a single noun-like entity within a sentence. A Noun Clause contains a subject and verb and can do anything that a noun can do:

What he does for this town is a blessing.

A Noun Phrase, frequently a noun accompanied by modifiers, is a group of related words acting as a noun: the oil depletion allowance; the abnormal, hideously enlarged nose.

There is a separate section on word combinations that become Compound Nouns — such as daughter-in-law, half-moon, and stick-in-the-mud.