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Re: The word "κορόιδευαν" and position of accent
by Greg Brush - Monday, 5 June 2017, 12:35 PM
  In contemporary monotonic accentuation the accent on the ο of όι indicates that the two letters are not the Greek digraph οι now pronounced "ee" (/i/); rather, the two letters are pronounced separately and with the first one stressed.

However, όι in the verbform κορόιδευαν is not pronounced as two completely separate vowels ο and ι, it is pronounced as the diphthong "oi" (/oj/). Since ρο and ι in κορόιδευαν represent one syllable ("roy", /roj/), the accent is not on the fourth syllable from the end. Thus the imperfect of the verb κοροϊδεύω is κορόιδευα, /ko-roj-δe-va/, while the simple past is κορόιδεψα, /ko-roj-δe-psa/, where my underline indicates the spoken stress.

For a little more about monotonic accentuation and diphthongs, take a look at the Modern Greek portion of Harry Foundalis' page "Accent Marks denoting Stress in Greek, and Other Diacritics".

Greg Brush