The Descriptive Phrase

The first thing to note about the descriptive phrase in Arabic is that the structure is inverted compared to English. In English, we would say 'tall boy', when describing a boy who is tall. The word 'tall' is the adjective (the description), and the word 'boy' is the noun being described. The order of the words is Adjective + Noun.

In Arabic, it's the other way around. The noun being described comes first, followed by the adjective. The word for 'boy' in Arabic is وَلَدٌ and the word for 'tall' is طَوِيْلٌ. So 'tall boy' in Arabic would be:

وَلَدٌ طَوِيْلٌ

For a descriptive phrase to be valid, the adjective and the noun need to match each other in four aspects:

1. Gender
2. Number
3. Definiteness
4. Grammatical State

For the examples which follow, do not worry about how the correct gender, number, state, etc. are constructed. That will come later. What's important is you remember that both the noun and the adjective need to match.

Gender

Nouns in Arabic have gender. They are either masculine or feminine. If an adjective is describing a noun, the adjective needs to match the noun's gender.

Number

Nouns also have a number. They are either singular, dual, or plural. Both the noun and the adjective need to match in number.

Definiteness

When something is definite, it refers to something specific, whereas indefinite is when something is generic. It is the difference between saying, "The boy," and "A boy." The most common way of making a word definite in Arabic is by prefixing الْ to it and removing the tanween. وَلَدٌ - a boy, becomes الْوَلَدُ - the boy

وَلَدٌ طَوِيْلٌ - a tall boy
الْوَلَدُ الطَّوِيْلُ - the tall boy

Grammatical State

The grammatical states of words are reflected by the last vowel on the word. Dammah, Fathah, and Kasrah represent the grammatical states of Raf', Nasb, and Jarr respectively.