Arabic Letter Tha

It sounds like the “th” in “think.” In pronunciation notation, that sound is /θ/. The letter's name is also written thāʾ or ṯāʾ in Latin letters.

Pronunciation varies by language and dialect. Egyptian Arabic may use “t” in everyday vocabulary and “s” in more formal or learned words. Persian and Urdu retain ث in some Arabic-derived spellings, but pronounce it as “s.”

Why ث has three dots

Arabic writing developed from Nabataean Aramaic, an earlier writing tradition. Inscriptions with a full Arabic letter repertoire are attested by the late fifth century CE.

In early undotted Arabic, ب, ت, and ث could share the same basic written skeleton. Distinguishing dots became common by the late seventh century CE, making these different consonants easier to tell apart.