Ah, grammar drives me mad in many cases, and it is actually one thing that bothers me with this game.
Mostly that is due to "quantums" being used, when quanta is the actual plural, but it is a bit odd, considering "quanta" is used on some cards, and "quantums" on others.
As far as nova goes, novae would be the plural in my book. English really keeps those (now) irregular plurals, just as they were.
As for electrum, can you give a situation where you would ever use a plural of it? I can't seem to think of a situation in which I have used "golds," for instance...we just don't need the plural of certain things. Even thinking of a metal from different locations, I would still use the singular...
Isn't English fun?
