How would you define 'noun'?

The definition of a 'noun' is best captured by stating that it is a word that represents a person, place, thing, or idea. Nouns serve as the building blocks of sentences, allowing us to name and identify everything around us. For instance, "cat" is a noun that represents a specific animal, while "London" is a noun that signifies a particular city. Additionally, nouns can signify abstract concepts such as "freedom" or "happiness." This broad definition encompasses all types of nouns, including proper nouns (specific names of people or places) and common nouns (general names for a person, place, or thing), highlighting their essential role in communication.

The other choices do not accurately reflect the function of nouns; for example, a word that describes an action refers to verbs, while adjectives modify nouns rather than represent them. A formal writing structure pertains to formats or styles of writing rather than to the parts of speech.