There's no single ending that makes a word a noun. Instead, nouns can end with a wide variety of letters and combinations:
* Vowels: cat, tree, house, sky
* Consonants: book, chair, dog, wall
* -s: books, chairs, dogs, walls
* -ing: running, singing, swimming, painting
* -ness: kindness, happiness, darkness, sadness
* -tion: action, education, information, attention
The key to identifying a noun is its function in a sentence. Nouns typically act as the subject, object, or complement of a verb. They can also be the object of a preposition.
Here are some examples:
* The cat sat on the mat. (Both "cat" and "mat" are nouns)
* John threw the ball. (Both "John" and "ball" are nouns)
* She is a doctor. ("She" is a noun, and "doctor" is a noun used as a complement)
If you're unsure whether a word is a noun, try to understand its role in the sentence. If it names a person, place, thing, or idea, it's likely a noun.