etacism

from The Century Dictionary.

• noun The Erasmian pronunciation of ancient Greek, characterized by giving the letter η its ancient sound of a in mate or ey in they: opposed to iotacism, the Reuchlinian and modern Greek method, which gives to η and to some other vowels and some diphthongs the sound of e in be or i in machine.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Greek Gram.) The pronunciation of the Greek η (eta) like the Italian e long, that is like a in the English word ate. See itacism.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun grammar The pronunciation of the Greek eta like the Italian long e, or the vowel in the English word ate.