noun (noun): a word (except a pronoun) that identifies a person, place or thing, or names one of them (proper noun)

The simple definition is: a person, place or thing. Here are some examples:

  • person : man, woman, teacher, John, Mary
  • place : home, office, town, countryside, America
  • thing : table, car, banana, money, music, love, dog, monkey
Note that any of the above can also be referred to by a pronoun. And note that names like John or America are called "proper nouns".

The problem with the simple definition above is that it does not explain why "love" is a noun but can also be a verb.

Another (more complicated) way of recognizing a noun is by its:

  1. ending
  2. position
  3. function

1. Noun ending

There are certain word endings that show that a word is a noun, for example:

  • -ity → nationality
  • -ment → appointment
  • -ness → happiness
  • -ation → relation
  • -hood → childhood

But this is not true for the word endings of all nouns. For example, the noun "spoonful" ends in -ful, but the adjective "careful" also ends in -ful.

2. Position in sentence

We can often recognise a noun by its position in the sentence.

Nouns often come after a determiner (a determiner is a word like a, an, the, this, my, such):

  • relief
  • an  afternoon
  • the  doctor
  • this word
  • my house
  • such  stupidity

Nouns often come after one or more adjectives:

  • a great relief
  • a peaceful afternoon
  • the tall, Indian doctor
  • this difficult word
  • my brown and white house
  • such  crass  stupidity

3. Function in a sentence

Nouns have certain functions (jobs) in a sentence, for example:

  • subject of verb: Doctors  work hard.
  • object of verb: He likes coffee.
  • subject and object of verb: Teachers teach students.

But the subject or object of a sentence is not always a noun. It could be a pronoun or a phrase. In the sentence "My doctor works hard", the noun is "doctor" but the subject is "My doctor".

 

sources: https://www.englishclub.com/grammar/noun-what.htm