Note the stress is on the third syllable. My bilingual dictionaries translate it as “Act of God” and/or “force majeure”. Babiniotis reduces the drama by giving the first definition thus: “ο παράγοντας (συνήθ απρόβλεπτος) που προβάλλει ανυπέρβλητα εμπόδια, ανατρέπει σχέδια, προγράμματα…” In other words, “unforeseen circumstances”.
I knew the Act of God meaning, so I was surprised to see it used in such a mundane context in this article: https://www.rthess.gr/politismos-ekdiloseis/akyronetai-megali-synavlia-sti-chalkidiki/ which contained the words: η συναυλία ματαιώνεται «λόγω ανωτέρας βίας». I wondered if Maria Farandouri had been whisked off to heaven by a volcanic eruption or a tidal wave.
The story is similar with αλκυονίδες μέρες. What English speakers understand as Halcyon Days (an idealised time in the past) is the secondary meaning in Greek. One autumn many years ago, I was in the car with my father-in-law. The weather was beautiful, “Αλκυονίδες μέρες, αλκυονίδες μέρες,” he said, which I interpreted as an Indian summer. Here is one definition: “An Indian summer is a period of unseasonably warm, calm, and clear weather that occurs in the autumn, typically in October or November, after the first autumn frost. The term describes a “summer-like” or “autumnal warmth” that appears to be a brief return of summer before winter truly sets in.”
I am quite happy with Indian Summer as a translation, but Babiniotis’s primary definition is much less flexible in terms of time: η ηλιόλουστες ημέρες που διακόπτουν τη χειμερινή κακοκαιρία κατά την τελευταία εβδομάδα του Δεκέμβριου , τις δυο τελευταίες του Ιανουάριου (κυρίως) και τη δεύτερη του Φεβρουάριου.
I have the impression that it was a November day when I was with my father-in-law, so I will stick to Indian Summer as a valid translation.