Tha (Indic)

Tha is a consonant of Indic abugidas. In modern Indic scripts, tha is derived from the early "Ashoka" Brahmi letter after having gone through the Gupta letter .
Āryabhaṭa numeration.
Aryabhata used Devanagari letters for numbers, very similar to the Greek numerals, even after the invention of Indian numerals. The values of the different forms of थ are: 
Historic Tha.
There are three different general early historic scripts - Brahmi and its variants, Kharoṣṭhī, and Tocharian, the so-called "slanting Brahmi". Tha as found in standard Brahmi, was a simple geometric shape, with variations toward more flowing forms by the Gupta . The Tocharian Tha did not have an alternate Fremdzeichen form. The third form of tha, in Kharoshthi () was probably derived from Aramaic separately from the Brahmi letter.
Brahmi Tha.
The Brahmi letter , Tha, is probably derived from the Aramaic Teth , and is thus related to the modern Greek Theta. Several identifiable styles of writing the Brahmi Tha can be found, most associated with a specific set of inscriptions from an artifact or diverse records from an historic period. As the earliest and most geometric style of Brahmi, the letters found on the Edicts of Ashoka and other records from around that time are normally the reference form for Brahmi letters, with vowel marks not attested until later forms of Brahmi back-formed to match the geometric writing style.
Tocharian Tha.
The Tocharian letter is derived from the Brahmi , but does not have an alternate Fremdzeichen form.
Kharoṣṭhī Tha.
The Kharoṣṭhī letter is generally accepted as being derived from the Aramaic Teth , and is thus related to Theta, in addition to the Brahmi Tha.
Devanagari Tha.
Tha (थ) is a consonant of the Devanagari abugida. It ultimately arose from the Brahmi letter , after having gone through the Gupta letter . Letters that derive from it are the Gujarati letter થ, and the Modi letter 𑘞.
Devanagari-using Languages.
In all languages, थ is pronounced as or when appropriate. Like all Indic scripts, Devanagari uses vowel marks attached to the base consonant to override the inherent /ə/ vowel:
Conjuncts with थ.
Devanagari exhibits conjunct ligatures, as is common in Indic scripts. In modern Devanagari texts, most conjuncts are formed by reducing the letter shape to fit tightly to the following letter, usually by dropping a character's vertical stem, sometimes referred to as a "half form". Some conjunct clusters are always represented by a true ligature, instead of a shape that can be broken into constituent independent letters. Vertically stacked conjuncts are ubiquitous in older texts, while only a few are still used routinely in modern Devanagari texts. The use of ligatures and vertical conjuncts may vary across languages using the Devanagari script, with Marathi in particular preferring the use of half forms where texts in other languages would show ligatures and vertical stacks.
Ligature conjuncts of थ.
True ligatures are quite rare in Indic scripts. The most common ligated conjuncts in Devanagari are in the form of a slight mutation to fit in context or as a consistent variant form appended to the adjacent characters. Those variants include Na and the Repha and Rakar forms of Ra. Nepali and Marathi texts use the "eyelash" Ra half form for an initial "R" instead of repha.
Stacked conjuncts of थ.
Vertically stacked ligatures are the most common conjunct forms found in Devanagari text. Although the constituent characters may need to be stretched and moved slightly in order to stack neatly, stacked conjuncts can be broken down into recognizable base letters, or a letter and an otherwise standard ligature.
Bengali Tha.
The Bengali script থ is derived from the Siddhaṃ , and is marked by a similar horizontal head line, but less geometric shape, than its Devanagari counterpart, थ. The inherent vowel of Bengali consonant letters is /ɔ/, so the bare letter থ will sometimes be transliterated as "tho" instead of "tha". Adding okar, the "o" vowel mark, gives a reading of /t̪ʰo/.
Like all Indic consonants, থ can be modified by marks to indicate another (or no) vowel than its inherent "a".
থ in Bengali-using languages.
থ is used as a basic consonant character in all of the major Bengali script orthographies, including Bengali and Assamese. 
Conjuncts with থ.
Bengali থ exhibits conjunct ligatures, as is common in Indic scripts, with a tendency towards stacked ligatures.
Gujarati Tha.
Tha (થ) is the seventeenth consonant of the Gujarati abugida. It is derived from the Devanagari Tha with the top bar (shiro rekha) removed, and ultimately the Brahmi letter .
Gujarati-using Languages.
The Gujarati script is used to write the Gujarati and Kutchi languages. In both languages, થ is pronounced as or when appropriate. Like all Indic scripts, Gujarati uses vowel marks attached to the base consonant to override the inherent /ə/ vowel:
Conjuncts with થ.
Gujarati થ exhibits conjunct ligatures, much like its parent Devanagari Script. Most Gujarati conjuncts can only be formed by reducing the letter shape to fit tightly to the following letter, usually by dropping a character's vertical stem, sometimes referred to as a "half form". A few conjunct clusters can be represented by a true ligature, instead of a shape that can be broken into constituent independent letters, and vertically stacked conjuncts can also be found in Gujarati, although much less commonly than in Devanagari.
True ligatures are quite rare in Indic scripts. The most common ligated conjuncts in Gujarati are in the form of a slight mutation to fit in context or as a consistent variant form appended to the adjacent characters. Those variants include Na and the Repha and Rakar forms of Ra.
Telugu Tha.
Tha (థ) is a consonant of the Telugu abugida. It ultimately arose from the Brahmi letter . It is closely related to the Kannada letter ಥ. Most Telugu consonants contain a v-shaped headstroke that is related to the horizontal headline found in other Indic scripts, although headstrokes do not connect adjacent letters in Telugu. The headstroke is normally lost when adding vowel matras.
Telugu conjuncts are created by reducing trailing letters to a subjoined form that appears below the initial consonant of the conjunct. Many subjoined forms are created by dropping their headline, with many extending the end of the stroke of the main letter body to form an extended tail reaching up to the right of the preceding consonant. This subjoining of trailing letters to create conjuncts is in contrast to the leading half forms of Devanagari and Bengali letters. Ligature conjuncts are not a feature in Telugu, with the only non-standard construction being an alternate subjoined form of Ṣa (borrowed from Kannada) in the KṢa conjunct.
Malayalam Tha.
Tha (ഥ) is a consonant of the Malayalam abugida. It ultimately arose from the Brahmi letter , via the Grantha letter "Tha". Like in other Indic scripts, Malayalam consonants have the inherent vowel "a", and take one of several modifying vowel signs to represent syllables with another vowel or no vowel at all.
Conjuncts of ഥ.
As is common in Indic scripts, Malayalam joins letters together to form conjunct consonant clusters. There are several ways in which conjuncts are formed in Malayalam texts: using a post-base form of a trailing consonant placed under the initial consonant of a conjunct, a combined ligature of two or more consonants joined together, a conjoining form that appears as a combining mark on the rest of the conjunct, the use of an explicit candrakkala mark to suppress the inherent "a" vowel, or a special consonant form called a "chillu" letter, representing a bare consonant without the inherent "a" vowel. Texts written with the modern reformed Malayalam orthography, "put̪iya lipi", may favor more regular conjunct forms than older texts in "paḻaya lipi", due to changes undertaken in the 1970s by the Government of Kerala.
Odia Tha.
Tha (ଥ) is a consonant of the Odia abugida. It ultimately arose from the Brahmi letter , via the Siddhaṃ letter "Tha". Like in other Indic scripts, Odia consonants have the inherent vowel "a", and take one of several modifying vowel signs to represent syllables with another vowel or no vowel at all. Like other Oriya letters with an open top, ଥ takes the subjoined matra form of the vowel "i" (ଇ):
As is common in Indic scripts, Odia joins letters together to form conjunct consonant clusters. The most common conjunct formation is achieved by using a small subjoined form of trailing consonants. Most consonants' subjoined forms are identical to the full form, just reduced in size, although a few drop the curved headline or have a subjoined form not directly related to the full form of the consonant. The second type of conjunct formation is through pure ligatures, where the constituent consonants are written together in a single graphic form. ଥ generates conjuncts only by subjoining and does not form ligatures. The subjoined form of ଥ is identical to a subjoined form of Cha used in limited contexts.
Comparison of Tha.
The various Indic scripts are generally related to each other through adaptation and borrowing, and as such the glyphs for cognate letters, including Tha, are related as well.
Character encodings of Tha.
Most Indic scripts are encoded in the Unicode Standard, and as such the letter Tha in those scripts can be represented in plain text with unique codepoint. Tha from several modern-use scripts can also be found in legacy encodings, such as ISCII.