Indefinite nouns take no article prefixed to them. However, the indefinite status of a noun can be denoted with a diacritical mark placed at the end of the word. To say “a car”, you can say سيارةً (siyaaratan). Here the ta’marbuta takes the “t” sound and the diacritical mark adds the “an” sound to the word, making it “siyaaratan”. This diacritical mark is called a tanwin. The use of this sound at the end of words to denote indefinite status is also known as nunation.

The mark is a double fatha, which makes the sound at the end of the word, “an” and not “un” or “in”. In this example (سيارةً), the tanwin sits atop the ta’marbuta at the end of the word.

For words that do not end in a ta’marbuta, such as كتاب, an alif (ا) is attached at the end of the word, and the tanwin is placed atop the alif. For example, كتاباً (kitaban), which means “a book”. Words ending in a hamza (ء), alif (ا), or alif maqsura (ى) do not require an alif attached.

In some grammatical situations, the indefinite mark will instead be a double damma (سيارةٌ) “siyaaratun” or a double kasra (سيارةٍ) “siyaaratin”. For double damma or double kasra endings, an added seath (alif) is not needed.