O in the context of "Bullet (typography)"

A bar or stroke is a modification consisting of a line drawn through a grapheme. It may be used as a diacritic to derive new letters from old ones, or simply as an addition to make a grapheme more distinct from others. It can take the form of a vertical bar, slash, or crossbar.

A stroke is sometimes drawn through the numerals 7 (horizontal overbar) and 0 (overstruck foreslash), to make them more distinguishable from the number 1 and the letter O, respectively. (In some typefaces, one or other or both of these characters are designed in these styles; they are not produced by overstrike or by combining diacritic. The normal way in most of Europe to write the number seven is with a bar. )

Omicron (US: /ˈoʊmɪkrɒn, ˈɒmɪkrɒn/ , UK: / oʊˈmaɪkrɒn/; uppercase Ο, lowercase ο, Greek: όμικρον) is the fifteenth letter of the Greek alphabet. This letter is derived from the Phoenician letter ayin: . In classical Greek, omicron represented the close-mid back rounded vowel [o] in contrast to omega, which represented the open-mid back rounded vowel [ɔː], and the digraph ⟨ου⟩ which represented the long close back rounded vowel [uː]. In modern Greek, both omicron and omega represent the mid back rounded vowel [o̞]. Letters that arose from omicron include Roman O and Cyrillic O and Ю. The name of the letter was originally οὖ (oû [ûː]), but it was later changed to ὂ μικρόν (ò mikrón 'small o') in the Middle Ages to distinguish the letter from omega ⟨ω⟩, whose name means 'big o', as both letters had come to be pronounced [o]. In modern Greek, its name has fused into όμικρον (ómikron). In the system of Greek numerals, it has a value of 70.

Œ (minuscule: œ), in English known as ethel or œthel (also spelt ēðel or odal), is a Latin alphabet grapheme, a ligature of o and e. In medieval and early modern Latin, it was used in borrowings from Greek that originally contained the diphthong οι, and in a few non-Greek words. These usages continue in English and French. In French, the words that were borrowed from Latin and contained the Latin diphthong written as œ now generally have é or è; but œ is still used in some non-learned French words, representing open-mid front rounded vowels, such as œil ("eye") and sœur ("sister").

It is used in the modern orthography for Old West Norse and is used in the International Phonetic Alphabet to represent the open-mid front rounded vowel. In English runology, œ ɶ is used to transliterate the rune othala ᛟ (Old English: ēðel, "estate, ancestral home"), of which English derives its name.

Ö, or ö, is a character that represents either a letter from several extended Latin alphabets, or the letter "o" modified with an umlaut or diaeresis. Ö, or ö, is a variant of the letter O. In many languages, the letter "ö", or the "o" modified with an umlaut, is used to denote the close- or open-mid front rounded vowels [ø] or [œ] ; compare the vowel in "girl", which in these languages phonetically could be written: /görl/. In languages without such vowels, the character is known as an "o with diaeresis" and denotes a syllable break, wherein its pronunciation remains an unmodified [o].

The open-mid front rounded vowel, or low-mid front rounded vowel, is a type of vowel sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents the sound is ⟨œ⟩. The symbol œ is a lowercase ligature of the letters o and e. The letter ⟨ɶ⟩, a small capital version of the ⟨Œ⟩ ligature, is used for a different vowel sound: the open front rounded vowel.