What does eta mean?
Eta is the seventh letter of the Greek alphabet, written as a capital Η and a lowercase η. In ancient Greek it came to represent a long open-mid vowel sound, having originally served as the letter H in earlier alphabets, and its name has passed into English as a standard way of referring to the character. Beyond language study, eta has become a workhorse symbol across the sciences: mathematicians use it for various constants and functions, physicists employ it to denote quantities such as efficiency and viscosity, and statisticians use measures like eta squared to express effect size. Because Greek letters are so widely adopted in technical fields, eta is encountered most often by students and professionals in mathematics, physics, engineering, and statistics rather than in everyday speech. Its pronunciation differs between British English (/ˈiːtə/) and American English (/ˈeɪtə/). As one of the foundational letters inherited from the Phoenician alphabet, eta forms part of a family that includes familiar names such as alpha, beta, gamma, and delta, all of which share the same ancient origin and continue to shape modern scientific notation.
The seventh letter of the Greek alphabet (Η, η).
"Eta comes after zeta and before theta."
Lowercase when referring to the letter itself.
A symbol used in mathematics and science, particularly denoting efficiency or viscosity in physics.
"The engine's efficiency was written using the symbol eta."
Regular English plural, used when referring to multiple instances of the letter.
"The manuscript contained several stray etas where the scribe had hesitated."
The Greeks gave eta two sounds over the centuries: it was once pronounced like our 'h' before classical Athens turned it into a long 'ay' — which is why Latin borrowed it as the letter H.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of eta
The word "eta" comes from the Ancient Greek name ἦτα for the letter, whose ultimate source is the Phoenician letter heth, which represented a breathy h sound. Early Greek alphabets used the sign for /h/, but in Ionic and Attic dialects, where the /h/ sound disappeared, the letter was repurposed to denote the long vowel /ɛː/. The Romans later took the western Greek form of the letter into Latin as H, preserving its original consonantal value. The English word "eta" is simply the Greek name adopted directly, first recorded in English usage as knowledge of the Greek alphabet became widespread.
How eta is actually used
Pronunciation varies by region and context: /ˈiːtə/ is common in British English, while /ˈeɪtə/ predominates in American English. The word is normally lowercased when referring to the letter itself; the all-caps form "ETA" belongs to unrelated abbreviations. It appears chiefly in academic, mathematical, scientific, and linguistic contexts rather than everyday conversation.
Easily confused with eta
"Eta" is a Greek letter, whereas "ETA" in capitals is an abbreviation for estimated time of arrival (or the Basque separatist organization Euskadi Ta Askatasuna).