NA particle meaning?


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?](https://japanese.stackexchange.com/questions/19180/are-%E3%81%AA-
and-%E3%81%A0-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".

