Theta (, , uppercase àor ô; lowercase ø; cursive ÃÂ; thÃÂÃÂta ; Modern: thëÃÂta ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth ð¤Â. In the system of Greek numerals, it has a value of 9.
In Ancient Greek, ø originally represented the aspirated voiceless dental plosive , but it later became a voiceless dental fricative , which is the value it retains in Modern Greek.
In its archaic form, ø was written as a cross within a circle (as in the Etruscan or ), and later, as a line or point in circle ( or ).
In modern print, lowercase theta may appear in two different forms: one resembling the uppercase form, like a zero with a horizontal bar through it, and one more cursive style featuring an open loop, resembling a nine. For use as a mathematical symbol, where the difference between the two forms may be significant, a dedicated Unicode symbol was introduced, which always displays the open-loop form. There is also , which differs from most realizations of the normal textual uppercase letter by having a cross-bar that goes all the way across, touching the outer O-shape on both sides.
In the Latin script used for the Gaulish language, theta inspired the tau gallicum (ê êÂÂ). The phonetic value of the tau gallicum is thought to have been . In addition, multiple modern languages written in Latin script use Latin theta.
The early Cyrillic letter fita (ò, ó) developed from ø. This letter existed in the Russian alphabet until the 1918 Russian orthography reform.
In the International Phonetic Alphabet (IPA), represents the voiceless dental fricative, as in thigh (), thick (), enthuse (), thing (), think (), thin (), thang (), myth (), smith (), youth (), bath (), math (), birth (), fourth (), death (), or health (). It does not represent the consonant in the, which is the voiced dental fricative counterpart, represented in the IPA by (cf. Eth). A similar-looking lower-case symbol, , which is called barred o, is the IPA symbol for the close-mid central rounded vowel.
The lowercase letter ø is used as a symbol for:
The uppercase letter ÃÂ is used as a symbol for:
In ancient times, Tau was used as a symbol for life or resurrection, whereas the eighth letter of the Greek alphabet (ninth in the archaic form anciently used for numeration), theta, was considered the symbol of death. A quotation attributed to the ancient Roman author Ennius (though possibly spuriously) said of it: "oh, theta, a letter much unluckier than the others".
According to Porphyry of Tyros, the Egyptians used an X within a circle as a symbol of the soul; having a value of nine, it was used as a symbol for Ennead. Johannes Lydus says that the Egyptians used a symbol for Kosmos in the form of theta, with a fiery circle representing the world, and a snake spanning the middle representing Agathos Daimon (literally: good spirit).
In classical Athens, it was used as an abbreviation for the Greek øìýñÃÂÿà(Thanatos, "death") and as it vaguely resembles a human skull, theta was used as a warning symbol of death, in the same way that skull and crossbones are used in modern times. It survives on potsherds used by Athenians when voting for the death penalty. Petrus de Dacia in a document from 1291 relates the idea that theta was used to brand criminals as empty ciphers, and the branding rod was affixed to the crossbar spanning the circle. For this reason, the use of the number 9 was sometimes avoided where the connotation was felt to be unluckyâÂÂthe mint marks of some Late Imperial Roman coins famously have the sum ÃÂàor ÃÂà(delta and epsilon, that is 4 and 5) substituted as a euphemism where a à(9) would otherwise be expected.