Taw is believed to be derived from the Egyptian hieroglyph meaning "mark"
The letter is named tāʼ . It is written in several ways depending on its position in the word:
Final ـَتْ (fathah, then tāʼ with a sukun on it, pronounced /at/, though diacritics are normally omitted) is used to mark feminine gender for third-person perfective/past tense verbs, while final تَ (tāʼ-fatḥah, /ta/) is used to mark past-tense second-person singular masculine verbs, final تِ (tāʼ-kasrah, /ti/) to mark past-tense second-person singular feminine verbs, and final تُ (tāʼ-ḍammah, /tu/) to mark past-tense first-person singular verbs. The plural form of Arabic letter ت is tāʼāt (تاءات), a palindrome.
Recently the isolated ت has been used online as an emoticon, because it resembles a smiling face.
An alternative form called tāʼ marbūṭah (تاء مربوطة, "bound tāʼ ") is used at the end of words to mark feminine gender for nouns and adjectives. It denotes the final sound /-a/ and, when in construct state, /-at/. Regular tāʼ, to distinguish it from tāʼ marbūṭah, is referred to as tāʼ maftūḥah (تاء مفتوحة, "open tāʼ ").
In words such as risālah رسالة ('letter, message'), tāʼ marbūṭah is denoted as h, and pronounced as /-a(h)/. Historically, it was pronounced as the /t/ sound in all positions, but in coda positions it eventually developed into a weakly aspirated /h/ sound (which is why tāʼ marbūṭah looks like a hāʼ (ه)); this /h/ itself was eventually left pronounced. When a word ending with a tāʼ marbūṭah is suffixed with a grammatical case ending or (in Modern Standard Arabic or the dialects) any other suffix, the /t/ is clearly pronounced. For example, the word رسالة ('letter, message') is pronounced as risāla(h) in pausa but is pronounced risālatu in the nominative case (/u/ being the nominative case ending). The pronunciation is /t/, just like a regular tāʼ (ت), but the identity of the "character" remains a tāʼ marbūṭah. Note that the isolated and final forms of this letter combine the shape of hāʼ and the two dots of tāʼ .
When words containing the symbol are borrowed into other languages written in the Arabic alphabet (such as Persian), tāʼ marbūṭah usually becomes either a regular ه or a regular ت.
Hebrew spelling: תָו
The letter tav in modern Hebrew usually represents a voiceless alveolar plosive: /t/.
The letter tav is one of the six letters which can receive a dagesh kal diacritic, besides bet, gimel, dalet, kaph and pe. Three of them – bet, kaph and pe – have their sound values changed in modern Hebrew from the fricative to the plosive by adding a dagesh. In modern Hebrew, the other three – including tav – do not change their pronunciation with or without a dagesh, but have had alternate pronunciations at other times and places.
In traditional Ashkenazi pronunciation, tav represents an /s/ without the dagesh, and has the plosive form when it has the dagesh. In some Sephardi areas, some Chassidic groups, as well as Yemen, tav without a dagesh represented a voiceless dental fricative /θ/, and tav with the dagesh is the plosive /t/. In traditional Italian pronunciation, tav without a dagesh is sometimes /s/ (for example in the word tallit that is pronounced talled).
In gematria, tav represents the number 400, the largest single number that can be represented without using the sophit (final) forms (see kaph, mem, nun, pe, and tzade).
In representing names from foreign languages, a geresh or chupchik can also be placed after the tav (ת׳), making it represent /θ/. (See also: Hebraization of English)
Tav is the last letter of the Hebrew word emet, which means 'truth'. The midrash explains that emet is made up of the first, middle, and last letters of the Hebrew alphabet (aleph, mem, and tav: אמת). Sheqer (falsehood), on the other hand, is made up of the 19th, 20th, and 21st (and penultimate) letters.
Thus, truth is all-encompassing, while falsehood is narrow and deceiving. In Jewish mythology it was the word emet that was carved into the head of the golem which ultimately gave it life. But when the letter aleph was erased from the golem's forehead, what was left was "met"—dead. And so the golem died.
Ezekiel 9:4 depicts a vision in which the tav plays a Passover role similar to the blood on the lintel and doorposts of a Hebrew home in Egypt. In Ezekiel’s vision, the Lord has his angels separate the demographic wheat from the chaff by going through Jerusalem, the capital city of ancient Israel, and inscribing a mark, a tav, “upon the foreheads of the men that sigh and that cry for all the abominations that be done in the midst thereof.”
In Ezekiel's vision, then, the Lord is counting tav-marked Israelites as worthwhile to spare, but counts the people worthy of annihilation who lack the tav and the critical attitude it signifies. In other words, looking askance at a culture marked by dire moral decline is a kind of shibboleth for loyalty and zeal for God.
"From aleph to taf" describes something from beginning to end, the Hebrew equivalent of the English "From A to Z."
In the Syriac alphabet, as in the Hebrew and Phoenician alphabets, taw (ܬ) is the last letter in the alphabet. It represents either /t/ (voiceless alveolar plosive) or between a /t/ and /d/ sound.