"There is no distinction between debate and combat to a dragon. Tinvaak los grah. For us it is one and the same." - paarthurnax

You could indeed use the words grah, krif, or vukein to refer to debate. In the English-Dragon dictionary, I've now added these words as possible translations for "debate."

An important point is that while all debate is battle, not all battle is debate. Paarthurnax's quote above is a good illustration of this; tinvaak los grah "speech is battle." The fact that this sentence can exist shows there is still a fundamental distinction between speech and battle.

There's not much we can do on the canon side of things, but on the non-canon side of things I've edited our own specific word for "debate" to graat to relate closer to grah "battle."