c. 1400, from Medieval Greek omega, from classical Greek o mega "big 'o' " (in contrast to o micron "little 'o' "); so called because the vowel was long in ancient Greek. From mega (see mega-). The final letter of the Greek alphabet, hence used figuratively for "the last, final" of anything (as in Rev. i:8),[omega etymology, omega origin, 英语词源]