Excellent definition of Noun.

Under use of English we are going to discuss eight part of speech with clear definition and examples, let's start. Eight part of speech as you knew :
Noun
.Pronoun
.Verb
.Adverb
.Adjective
.Preposition
.Conjuction
Interjections.
Before you speak English correctly you need to know these eight part of speech , now you are unable to make correct sentence because you cannot use these part of speech well. You know if a human being uses his /her legs to eat it is not correct. Let's pick one of them and discuss it; which that is noun.
Noun: a word  that is the name of something (such as a person, animals, thing, idea, quality, or action ) and is typically used in a sentence as subject or object of a verb or as object of a preposition.
Another definition of a noun.
1. When you mention a person name, e,g. Teacher, Johnson, Abraham that name is a noun
2. Also when you mentioned a place, e,g. Market, Post-office,  School, Kano, Hospital. Etc.
3.When you mention the name of an animal, eg. Dog, Goat, Cat, Donkey. Etc.

4. Finally when you mention a thing you mentioned a noun.

Let's move to the next step. 

Examples in sentence

1. You'd better see a doctor about that cough.

2. Abraham must do the assignment.

3. We need more money for roads, hospitals, and schools.

4. Kano state is the center of commerce in Nigeria.

5. They called him donkey when he refused to go along with their plans.

6. I could hear a dog barking.

7. She opened her bag(=her handbag) and took out the comb. 

8. He went into the house.

         Look very well we under lined each noun in these sentences .

References:

Oxford dictionary 7th edition.

Merriam Webster Dictionary.

‘A’-one  English 2001.