Definition of Noun Clause

A noun is used as a subject or an object.
A noun clause is used as a subject. In other words, a noun clause is used in the same ways as a noun.
A noun clause is a clause functioning as a noun. It has its own subject and verb.
Noun clauses perform eight main grammatical functions within sentences in the English language. Both native speakers and ESL students must learn the eight functions to fully and correctly use noun clauses in spoken and written English. The eight functions of noun clauses are:

1. Subject
2. Subject complement
3. Direct object
4. Object complement
5. Indirect object
6. Prepositional complement
7. Adjective phrase complement
8. Appositive

Noun clauses are defined as subordinate or dependent clauses formed by a subordinating conjunction followed by a clause. Noun clauses perform nominal functions, or functions prototypically performed by noun phrases.
Noun Clauses as Subjects

The first grammatical function that noun clauses can perform is the subject. Subjects are defined as words, phrases, and clauses that perform the action of or act upon the predicate. For example, the following italicized noun clauses function as subjects