Eta (; uppercase , lowercase ; Greek, Ancient (to 1453);: ἦτα ē̂ta in Greek, Modern (1453-); pronounced as /ɛ̂ːta/ or Greek, Modern (1453-);: ήτα ita in Greek, Modern (1453-); pronounced as /ˈita/) is the seventh letter of the Greek alphabet, representing the close front unrounded vowel, in Greek, Modern (1453-); pronounced as /i/. Originally denoting the voiceless glottal fricative, in Greek, Modern (1453-); pronounced as /h/, in most dialects of Ancient Greek, its sound value in the classical Attic dialect was a long open-mid front unrounded vowel, in Greek, Modern (1453-); pronounced as /ɛː/, which was raised to in Greek, Modern (1453-); pronounced as /i/ in Hellenistic Greek, a process known as iotacism or itacism.
In the ancient Attic number system (Herodianic or acrophonic numbers), the number 100 was represented by "", because it was the initial of Greek, Ancient (to 1453);: ΗΕΚΑΤΟΝ, the ancient spelling of Greek, Modern (1453-);: ἑκατόν = "one hundred". In the later system of (Classical) Greek numerals eta represents 8.
. Letters that arose from eta include the Latin H and the Cyrillic letters И and Й.See main article: Heta (letter). The letter shape 'H' was originally used in most Greek dialects to represent the voiceless glottal fricative, in Greek, Modern (1453-); pronounced as /h/. In this function, it was borrowed in the 8th century BC by the Etruscan and other Old Italic alphabets, which were based on the Euboean form of the Greek alphabet. This also gave rise to the Latin alphabet with its letter H.
Other regional variants of the Greek alphabet (epichoric alphabets), in dialects that still preserved the sound in Greek, Modern (1453-); pronounced as /h/, employed various glyph shapes for consonantal heta side by side with the new vocalic eta for some time. In the southern Italian colonies of Heracleia and Tarentum, the letter shape was reduced to a "half-heta" lacking the right vertical stem (Ͱ). From this sign later developed the sign for rough breathing or spiritus asper, which brought back the marking of the in Greek, Modern (1453-); pronounced as /h/ sound into the standardized post-classical (polytonic) orthography.[1] Dionysius Thrax in the second century BC records that the letter name was still pronounced heta (ἥτα), correctly explaining this irregularity by stating "in the old days the letter Η served to stand for the rough breathing, as it still does with the Romans."[2]
In the East Ionic dialect, however, the sound in Greek, Modern (1453-); pronounced as /h/ disappeared by the sixth century BC, and the letter was re-used initially to represent a development of a long open front unrounded vowel, in Greek, Modern (1453-); pronounced as /aː/, which later merged in East Ionic with the long open-mid front unrounded vowel, in Greek, Modern (1453-); pronounced as /ɛː/ instead.[3] In 403 BC, Athens took over the Ionian spelling system and with it the vocalic use of H (even though it still also had the in Greek, Modern (1453-); pronounced as /h/ sound itself at that time). This later became the standard orthography in all of Greece.
During the time of post-classical Koiné Greek, the in Greek, Modern (1453-); pronounced as /ɛː/ sound represented by eta was raised and merged with several other formerly distinct vowels, a phenomenon called iotacism or itacism, after the new pronunciation of the letter name as ita instead of eta.
Itacism is continued into Modern Greek, where the letter name is pronounced pronounced as /[ˈita]/ and represents the close front unrounded vowel, in Greek, Modern (1453-); pronounced as /i/. It shares this function with several other letters (ι, υ) and digraphs (ει, οι), which are all pronounced alike.
Eta was also borrowed with the sound value of pronounced as /[i]/ into the Cyrillic script, where it gave rise to the Cyrillic letter И.
In Modern Greek, due to iotacism, the letter (pronounced in Greek, Modern (1453-); pronounced as /ˈita/) represents a close front unrounded vowel, in Greek, Modern (1453-); pronounced as /i/. In Classical Greek, it represented the long open-mid front unrounded vowel, in Greek, Modern (1453-); pronounced as /ɛː/.
The uppercase letter Η is used as a symbol in textual criticism for the Alexandrian text-type (from Hesychius, its once-supposed editor).
In chemistry, the letter H as symbol of enthalpy sometimes is said to be a Greek eta, but since enthalpy comes from ἐνθάλπος, which begins in a smooth breathing and epsilon, it is more likely a Latin H for 'heat'.
In information theory the uppercase Greek letter Η is used to represent the concept of entropy of a discrete random variable.
The lowercase letter η is used as a symbol in:
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.