Key Difference: Noun is a part of speech that denotes a person, place, thing or idea. Adjectives are words that describe and give more information about a noun.
Nouns and adjectives are two different things, thought they both belong to the eight parts of speech, along with verbs, pronouns, adverbs, prepositions, conjunctions and interjections. The eight parts of the speech are the basis of the English language and one should know them when learning the language. There is a lot of confusion regarding the differences between these two.
Noun is a part of speech that denotes a person, place, thing or idea. Everything around us that can be named can be regarded as a noun. Nouns are primarily divided into proper noun and common noun. Specific names that represent unique entities are known as proper nouns, ex: Earth, Mary, England, Cambridge University, etc. When writing proper nouns, the first letter of the word is written in capital letter. Common nouns are names for general terms and describe a class of entities, ex: table, planet, country, etc. Common nouns are written in smaller case unless they are at the start of a sentence.
Other types of nouns also include count nouns, mass nouns, collective nouns and abstract nouns. Count nouns are nouns that can combine with numerals of quantifiers (ex: chair, table), it can also take an indefinite article, a or an (ex: a dozen buildings). Mass nouns or non-count nouns are objects that cannot be counted in numerical terms (water, milk, energy and furniture). Collective nouns refer to a group of one or more entities (ex: committee, herd, and group). Abstract nouns refer to objects that are not tangible, or abstracts such as ideas (ex: Love, hatred, anticipation and excitement).
Adjectives are words that describe and give more information about a noun (A very tall building). Adjectives can either precede the noun or succeed it in some cases. Adjectives can also be used to modify verbs (He sang quickly). Adjectives can be classified into four kinds of uses; attributive, predictive, absolute and nominal. Attributive adjectives usually precede the noun they modify and give a description to the noun (ex: I saw three sad puppies). Predictive adjectives are not part of the noun clause but is linked via a copula or other linking mechanism to the noun they modify (the kids are happy). Absolute adjectives usually modify the subject of a sentence or whatever noun they are closest to. Nominal adjectives are adjectives that act like nouns.