O (Indic)

Aryabhata used Devanagari letters for numbers, very similar to the Greek numerals, even after the invention of Indian numerals. The ो sign was used to modify a consonant's value ×10¹⁴, but the vowel letter ओ did not have an inherent value by itself.[1]

There are three different general early historic scripts - Brahmi and its variants, Kharoṣṭhī, and Tocharian, the so-called slanting Brahmi. O as found in standard Brahmi, was a simple geometric shape, with variations toward more flowing forms by the Gupta . Like all Brahmic scripts, Tocharian O has an accompanying vowel mark for modifying a base consonant. In Kharoṣṭhī, the only independent vowel letter is for the inherent A. All other independent vowels, including O are indicated with vowel marks added to the letter A.

Brahmi O

The Brahmi letter O , is probably derived from the altered Aramaic Waw , and is thus related to the modern Latin F, V, U, W, Y and Greek Upsilon.[2] Several identifiable styles of writing the Brahmi O can be found, most associated with a specific set of inscriptions from an artifact or diverse records from an historic period.[3] 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 some vowel marks not attested until later forms of Brahmi back-formed to match the geometric writing style.

Brahmi O historic forms

Ashoka (3rd-1st c. BCE)	Girnar (~150 BCE)	Kushana (~150-250 CE)	Gujarat (~250 CE)	Gupta (~350 CE)

Tocharian O

The Tocharian letter is derived from the Brahmi . Unlike some of the consonants, Tocharian vowels do not have a Fremdzeichen form.

Tocharian consonants with O vowel marks

Ko	Kho	Go	Gho	Co	Cho	Jo	Jho	Nyo	Ṭo	Ṭho	Ḍo	Ḍho	Ṇo
To	Tho	Do	Dho	No	Po	Pho	Bo	Bho	Mo	Yo	Ro	Lo	Vo
Śo	Ṣo	So	Ho

Devanagari independent Ō and Ō vowel sign.

Ō (ऒ) is a vowel 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 ઓ, and the Modi letter 𑘌.

Bengali independent Ō and Ō vowel sign.

Ō (ও) is a vowel of the Bengali abugida. It is derived from the Siddhaṃ letter , and is marked by the lack of horizontal head line and less geometric shape than its Devanagari counterpart, ऒ.

Gujarati independent O and O vowel sign.

Ō (ઓ) is a vowel of the Gujarati abugida. It is derived from the Devanagari Ō , and ultimately the Brahmi letter .

Gujarati Candra O

Gujarati independent short O and short O vowel sign.

Candra O (ઑ, short O) is a vowel of the Gujarati abugida. It is derived from the Devanagari Candra O, and ultimately the Brahmi letter .

Telugu independent vowel and vowel sign O.

O (ఒ) is a vowel of the Telugu abugida. It ultimately arose from the Brahmi letter . It is closely related to the Kannada letter ಒ. Like in other Indic scripts, Telugu vowels have two forms: and independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of Telugu consonant letters. Vowel signs in Telugu can interact with a base consonant in one of three ways: 1) the vowel sign touches or sits adjacent to the base consonant without modifying the shape of either 2) the vowel sign sits directly above the consonant, replacing its v-shaped headline, 3) the vowel sign and consonant interact, forming a ligature. Unlike other vowels, the O vowel sign has an alternate form in some typefaces that is used for the Gho, Jho, Mo and Yo syllables.

Telugu Gho and Ghō, showing the alternate forms of the vowel marks.

Telugu O vowel sign on క, ఖ, గ, ఘ & ఙ: Ko, Kho, Go, Gho and Ngo. Note that how the vowel sign interacts with the base consonant is dependent on the location of the headline, the absence of a headline, and the presence of a tail to attach to.

Telugu Ō

Telugu independent vowel and vowel sign Ō.

In addition, Telugu also contains a second O vowel, Ō (ఓ). It is also descended from the Brahmi letter . It is closely related to the Kannada letter ಓ. The long Ō vowel sign generally interacts with a base consonant the same as short O, with an alternate vowel sign form in some typefaces for Ghō, Jhō, Mō and Yō.

Telugu Ō vowel sign on క, ఖ, గ, ఘ & ఙ: Kō, Khō, Gō, Ghō and Ngō. Note that how the vowel sign interacts with the base consonant is dependent on the location of the headline, the absence of a headline, and the presence of a tail to attach to.

Malayalam independent vowel and vowel sign O.

O (ഒ) is a vowel of the Malayalam abugida. It ultimately arose from the Brahmi letter , via the Grantha letter o. Like in other Indic scripts, Malayalam vowels have two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters. Vowel signs in Malayalam usually sit adjacent to its base consonant - below, to the left, right, or both left and right, but are always pronounced after the consonant sound.

Malayalam Ō

Malayalam independent vowel and vowel sign Ō.

Ō (ഓ, Long O) is a vowel of the Malayalam abugida. It is a variation of the regular Malayalam short O vowel that appeared after Grantha. Like other Malayalam vowels, Ō has two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters.

Odia independent vowel and vowel sign O.

O (ଓ) is a vowel of the Odia abugida. It ultimately arose from the Brahmi letter , via the Siddhaṃ letter o. Like in other Indic scripts, Odia vowels have two forms: an independent letter for word and syllable-initial vowel sounds, and a vowel sign for changing the inherent "a" of consonant letters. Vowel signs in Odia usually sit adjacent to its base consonant - below, to the left, right, or both left and right, but are always pronounced after the consonant sound. No base consonants are altered in form when adding a vowel sign, and there are no consonant+vowel ligatures in Odia.