Definition. Adjective can be defined as a word which modifies a noun or pronoun. Here, the noun is a head word in a phrase or in a sentence.

Study this follows!

(a) I am happy.
(b) She is my cute baby.

in (a), the word happy is (pure) adjectives *). Happy modifies subjective pronoun (I). In (b), the word cute is an adjective and modifies the noun baby. In (a), adjective is used in a sentence, and in (b), cute is used in a phrase (cute baby).

Why To Modify
As a modifier, adjective has a main function to modify noun or pronoun. In other words, it gives a new information for the noun or the pronoun to make it more clearly for listeners or readers.

Noun as an Adjective
A noun can be as an adjective when it modifies (or give new information to) other noun in a phrase.

For examples:

Biology book

Biology is a noun and book is too. Which modifies which? Here, biology modifies book. When there is no biology, book does not have more clearly about what kinds of book it is.

Kinds of Adjectives
There are many kinds of adjectives in English, some of them are discussed below!

1. Adjective of Quality
2. Adjective of Quantity
3. Adjective of Number or Numeral Adjective

  • 3.1. Definite Numeral Adjective
  • 3.2. Indefinite Numeral Adjective
  • 3.3. Distributive Numeral Adjective
4. Demonstrative Adjective

Adjective of Quality is also called Descriptive Adjective. It shows kind or quality of a person or thing.
Example: He is a handsome man.

Adjective of Quantity shows how much of a thing is meant; (Wren & Martin, 1996). 
Example: I ate some rice.

Adjective of Number or Numeral Adjective shows how many persons or things are meant which is refered by a number, e.g. 1, 2, 3, etc.
Example: Hand has five fingers.

Adjective of number can also be devided into 3 kinds, they are:

(a) Definite Numeral Adjective. denotes an exact number.
e.g. one, two, three, etc

(b) Indefinite Numeral Adjective. does not denote an exact number.
e.g. All, some, few, many, several, etc

(c). Distributive Adjective. refers to each one of a number.
e.g. Each member should be re-registered before joining the team.

Demonstrative Adjective
Demonstrative adjective points out which person or thing is meant.
e.g. That lawyer was accused by the judge.

Addition. Question words can be said (in use) as an adjective as well when it is combined by a noun
e.g. What book does she want to buy?