Ṯāʾ

 (ث) is one of the six letters the Arabic alphabet added to the twenty-two from the Phoenician alphabet (the others being, , , , ). In Modern Standard Arabic it represents the voiceless dental fricative, also found in English as the "th" in words such as "thank" and "thin". In Persian, Urdu, and Kurdish it is pronounced as s as in "sister" in English. Ṯāʾ, along those with the letter ش|shīn, are the only two surviving Arabic letters with three dots above. In most European languages, it is mostly romanized as the digraph th. In other languages, such as Indonesian, this Arabic letter is often romanized as ts and Ṡ.

The most common transliteration in English is "th", e.g. Ethiopia (إثيوبيا), thawb (ثوب).

In name and shape, it is a variant of (ت). Its numerical value is 500 (see Abjad numerals).

The Arabic letter ث is named ثَاءْ ṯāʾ. It is written in several ways depending in its position in the word:

In contemporary spoken Arabic, pronunciation of ṯāʾ as is found in the Arabian Peninsula, Iraqi, and Tunisian and other dialects and in highly educated pronunciations of Modern Standard and Classical Arabic. Pronunciation of the letter varies between and within the various varieties of Arabic: while it is consistently pronounced as the voiceless dental plosive in Maghrebi Arabic (except Tunisian and eastern Libyan), on the other hand in the Arabic varieties of the Mashriq (in the broad sense, including Egyptian, Sudanese and Levantine) and Hejazi Arabic, it is pronounced as the sibilant voiceless alveolar fricative  in loanwords from Literary Arabic.

When representing this sound in transliteration of Arabic into Hebrew, it is written as ת׳.

Common Semitic perspective
The choice of the letter  as the base for this letter was not due to etymology (see History of the Arabic alphabet), but rather due to phonetic similarity. For other Semitic cognates of the phoneme  see Sound changes between Proto-Semitic and the daughter languages.

The South Arabian alphabet retained a symbol for  (𐩻).

Ethiopia is the only country name in Arabic that uses the letter ṯāʾ on their name.