What does the NA mean in this sentence?
Sonna baka NA koto...
そんなバカなことは、普通に言わないよ
Normally, (you) don't say such a stupid thing
What does the NA mean in this sentence?
Sonna baka NA koto...
そんなバカなことは、普通に言わないよ
Normally, (you) don't say such a stupid thing
For the etymology of both : Are な and だ both copula verbs?
In modern japanese, な is the modifying form of the copula and だ is its conclusive form.
So yeah, as Ringil said, it just means that バカ modifies こと : "a stupid thing".