η

η

1. (mathematics) The metric tensor in quantum field theory.
2. (chemistry, physics) The coefficient of viscosity.
3. (engineering) Efficiency in engineering.
4. (physics) Sommerfeld parameter.
5. (machine learning) Learning rate.
6. (UPA) alternative form of ŋ.

• η on Wikipedia.Wikipedia

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

η • (ē) (lowercase, uppercase Η)

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: /ɛː/. It is often transliterated as either e or i. It is preceded by ζ and followed by θ.

• η’ (i’), ,η (,i)
• h, H (Roman)
• и, И (Cyrillic)
• й, Й (Cyrillic)
• ⲏ, Ⲏ (Coptic)

• ἡ (hē, feminine article)
• ἥ (hḗ, feminine of pronoun ὅς)
• ᾖ (ēî, inflectional form of verb εἰμί)
• (Greek-script letters) Α α, Β β, Γ γ, Δ δ, Ε ε, Ζ ζ, Η η, Θ θ, Ι ι, Κ κ, Λ λ, Μ μ, Ν ν, Ξ ξ, Ο ο, Π π, Ρ ρ, Σ σ ς, Τ τ, Υ υ, Φ φ, Χ χ, Ψ ψ, Ω ω
• (non-Classical letters) Ϝ (W) ϝ (w), Ͷ ͷ, Ͱ (H) ͱ (h), Ϻ (S) ϻ (s), Ϟ ϟ, Ϙ (Q) ϙ (q), Ͳ (S) ͳ (s)
• (punctuation) · ;
• (diacritics) ᾿ ῾ ◌́ ◌̀ ῀ ¨

• IPA^(key): /i/ pronounced unstressed, together with its following word; compare to the stressed ή (í)
• Homophone: οι (oi)

From the vocalic usage of the Ancient Greek letter.

η • (i) (lowercase, uppercase Η)

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

• (Greek-script letters) Α α, Β β, Γ γ, Δ δ, Ε ε, Ζ ζ, Η η, Θ θ, Ι ι, Κ κ, Λ λ, Μ μ, Ν ν, Ξ ξ, Ο ο, Π π, Ρ ρ, Σ σ ς, Τ τ, Υ υ, Φ φ, Χ χ, Ψ ψ, Ω ω
• (non-Classical letters) Ϝ (W) ϝ (w), Ͷ ͷ, Ͱ (H) ͱ (h), Ϻ (S) ϻ (s), Ϟ ϟ, Ϙ (Q) ϙ (q), Ͳ (S) ͳ (s)
• (punctuation) · ;
• (diacritics) ᾿ ῾ ◌́ ◌̀ ῀ ¨

From Ancient Greek ἡ (hē).

η • (i)

1. (definite) feminine nominative singular of ο (o, “the”)