Mark J. Reed wrote:
> Someday I'll get back to conlanging instead of just exploiting y'all for 
> your linguistic expertise for other purposes.  Honest!
> Several calendars, starting with the ancient Egyptian, are solar with a 
> basic structure of 12 30-day months followed by 5 extra days called the 
> "epagomenae" (or "epagomenal days" in the boring English version).  
> Later revisions introduced the concept of leap years, in which there was 
> a 6th epagomenal day.  My question is simple: what's the singular form 
> of "epagomenae"?   Is it "epgagomena"? 


  It looks Greek in origin rather
> than Latin (although the -ae makes me suspicious; maybe it's a 
> Latinization of a Greek borrowing),

Spot on! It's a Latinized version of a Greek borrowing, which is quite
common practice in English. It is actually a passive participle in Greek
and is feminine because it agrees with the word for 'day' which, if
context is clear, can be omitted (or "understood"):
hai epagomenai [he:merai] = the intercalated [days]

he: epagomene: [he:mera:] = the intercalated [day]

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