In the ancient Roman calendar, the first day of each month; used in the phrase 'the Greek Calends' to mean something that will never happen.
From Latin Kalendae, possibly related to 'calare' (to call), because the first day was publicly announced. The word became famous through the phrase 'Greek Calends' (since Greeks didn't use this calendar system).
Romans said 'on the Greek Calends' the way we say 'when pigs fly'—it meant something impossible! This phrase became so common that Latin authors used it constantly to describe things that would never happen.
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