In reply to:
Is opera the other onliest word's got its own plural when it's already a plural?
Although I wouldn't have expressed the question in quite those words
, I understood Faldage to be making a distinction between "got its own plural" and "is its own plural", i.e. that opera (works) is the plural of opus (a work), but opera is also used in the singular sense of a musical drama, for which the plural is, presumably, operas, as in "I have seen three operas this year." Interestingly enough, although explicit in their listing of the two senses of opera, the online dictionaries were strangely silent on the plural of "an opera". It appears that a Latin plural has become an Italian singular??
Agenda is a word that is a plural (of agendum), but is often pluralized itself to agendas. The latter smacks of misuse of Latin to me, but some dictionaries seem to have accepted it. dictionary.com tries to justify it like this: http://www.dictionary.com/cgi-bin/dict.pl?term=agendas
(I even found the repugnant "agendums"!)
Doubtless there are other similar -um/-a/-as examples.
And humble apologies, Faldage, if I have misrepresented you.
