Adjectives are words that are used to modify a noun.
Example: green grass (the adjective "green" describes the noun "grass")

There are three kinds of adjectives known as the positive, comparative, and superlative forms, as in green, greener, greenest.

Adjectives can be grouped into seven categories:
nouns as adjectives
adjectives that modify an object
numbers as adjectives
pronouns and articles as adjectives
multiple adjectives
compound adjectives
adjectives used as nouns

:: Nouns as adjectives
A noun can be used to qualify (or describe) another noun, as in goose feathers, in which case there are no comparative or superlative forms such as "goosier" or "goosiest."

Some nouns can be made into an adjective by adding an ending such as -ish, -like, -ly, -y, -en, -al, -ar, -ory.

Examples:
He spoke in a childish manner.
My, what a womanly figure you have.
His teeth were yellowish in color.
He was sitting at a wooden desk.
He works at the main office.
What a spectacular show!
Our program is going through a transitory period.

Oftentimes, the endings -en and -al will be dropped, and the noun form will be used by itself, as in oak table, wool shirt, and coast line.
 

:: Adjectives that modify an object
Adjectives such as "like" and "worth" may be used to modify objects.

Examples:
Stale bread tastes like Styrofoam.
Your textbook is worth one dollar.

Sometimes prepositions like "of" and "with" are used to form adjectives.

Examples:
She is fearful of dogs.
Sometimes parents can be impatient with you.
 

:: Numbers as adjectives
Any words related to number are considered adjectives, including "two," "twenty," "few," "many," "dozen," "third," and so on.
 

:: Pronouns and articles as adjectives
Pronouns such as "this," "that," and "those" used to modify a noun are called demonstrative adjectives.

Possessive pronouns such as "my," "your," and "his" used to modify a noun are called possessive adjectives.

Articles such as "a," "an," and "the" are also adjectives.
 

:: Multiple adjectives
When using more than one adjective to modify a noun, the adjectives may be separated by a conjunction or by commas.

Examples:
Your teeth are strong and beautiful.
You have strong, beautiful teeth.
 

:: Compound adjectives
Nouns and adjectives may be combined to modify another noun, in which case the word can be hyphenated (although the hyphen is often a matter of personal preference).

Examples:
He is a warm-hearted fellow.
I can be empty-headed sometimes.
 

Past participles of verbs can also be used as adjectives, such as "native born," "foreign made," "soft spoken," "warmly dressed," "well behaved," and so on.
 

:: Adjectives used as nouns
It is possible to use an adjective as a noun by simply using the adjective as the subject and omitting the noun it modifies. Usually, adjectives used as nouns refer to a specific quality shared by a group (the pleasant) or a specific human characteristic shared by a group of people (the wise).

Example:
We moderns are to the ancients what the poor are to the rich.