لدي تسعة كتب.

لدي means something like with me, at my disposal, or in my possession. In this sentence, it is the natural way to express I have in formal or standard Arabic.

So the sentence is not built the same way as English. It is closer to There are nine books with me.

In Arabic, possession is often expressed without a normal verb like English have. Instead, Arabic commonly uses a word like لدى or عند plus a pronoun.

So:

• لدي تسعة كتب = literally With me are nine books
• natural English meaning = I have nine books

This is a very common Arabic pattern.

In fully marked writing, yes: لديَّ is the fully vocalized form.

What is happening is:

• base form: لدى
• plus ي = my / me
• pronunciation: ladayya

In everyday Arabic writing, short vowels and other diacritics are usually omitted, so you will often just see لدي.

Because numbers 3–10 follow a special gender rule in Arabic: the number usually takes the opposite gender of the counted noun.

Here the counted noun is كتب (books), and its singular is كتاب, which is masculine. Because of that, the numeral takes the feminine form:

• تسعة كتب = nine books

If the singular noun were feminine, you would normally use تسع instead.

When Arabic number rules depend on gender, you usually determine that gender from the noun’s singular form.

So even though the sentence uses the plural كتب, the grammar rule looks back to the singular:

• singular: كتاب = masculine
• therefore the numeral is تسعة

This is a very common source of confusion for learners.

Because after the numbers 3–10, the counted noun is normally plural in Arabic.

So:

• three books = ثلاثة كتب
• nine books = تسعة كتب

This is just the standard pattern for that number range. Other number ranges follow different rules.

In a fully vocalized version, the sentence would be:

لديَّ تِسْعَةُ كُتُبٍ

Here:

• تسعةُ is nominative
• كتبٍ is genitive

Why?

• The phrase لديَّ comes first and functions like with me
• the number phrase تسعة كتب is the main noun phrase of the sentence
• after numbers 3–10, the counted noun is normally plural genitive

Because normal Arabic writing usually leaves out short vowels and most case endings.

So although the full grammatical form is:

تِسْعَةُ كُتُبٍ

it is normally written simply as:

تسعة كتب

This is completely normal in Arabic texts.

Because the phrase means nine books, which is indefinite.

In this basic counting pattern, the counted noun is usually indefinite:

• تسعة كتب = nine books

If you wanted to say the nine books, Arabic would usually use a different structure, such as:

• الكتب التسعة

Yes, absolutely.

• عندي تسعة كتب is very common and natural, especially in speech.
• لدي تسعة كتب is also correct, but it often sounds a bit more formal or more written.

Both can mean I have nine books.

A careful full MSA pronunciation is:

ladayya tisʿatu kutubin

In less formal reading, without saying full case endings, you will often hear:

ladayya tisʿa kutub

A few pronunciation notes:

• لدي is pronounced ladayya
• the ʿ in tisʿa represents ع
• كتب is kutub, not kitab or kutib