Definition of "eta"

eta¹

/ˈiːtə/

noun
plural etas
1. The seventh letter of the Modern Greek alphabet, the eighth in Old Greek.
  Quotations
  Greek was an exercise in making the familiar strange. Its alphabet mapped onto the Roman alphabet, but only partly so, and often letters did not sound how they looked — a rho (Ρ) was not a P, and an eta (Η) was not an H.
  2022, R. F. Kuang, Babel, HarperVoyager, page 25
2. (physics) A kind of electrically neutral meson having zero spin and isospin.

eta²

/ˈeɪtə/

noun
plural etas or eta
1. A social outcast in Japan who is subjected to menial work, making up a class or caste of such people.

eta³

noun
plural etas
1. Alternative form of ita (“kind of palm tree”)