η

Symbol

 * 1)  The metric tensor in quantum field theory.
 * 2)  The coefficient of viscosity.
 * 3)  Efficiency in engineering.
 * 4)  Sommerfeld parameter.

Etymology
Derived from its majuscule counterpart Η, from the Phoenician letter 𐤇, heth.

Letter

 * 1) Lower-case eta, the seventh letter of the ancient Greek alphabet. Its name was ἦτα and it represented a long open-mid front unrounded vowel: . It is often transliterated as either e or i. It is preceded by ζ and followed by θ.

Pronunciation

 * pronounced unstressed, together with its following word; compare to the stressed

Etymology 1
From the vocalic usage of the Ancient Greek letter.

Letter

 * 1) Lower-case eta, the seventh letter of the modern Greek alphabet. Its name is ήτα and it represents a close front unrounded vowel: . It is often transliterated as either e or i. It is preceded by ζ and followed by θ.

Etymology 2
From.

Article

 * 1)   (the)