Getae and Dacians? Are they the same? Or is this unknowable?

[Justin of the New Yorkii]

Not sure from which come this Getae name, but greeks also used the term "Keltoi" for Celts, even if i dont think Celts ever call themsleves like that.

I get your point about the term Getae, but the first line of Caesar's De Bello Gallico says:
"All Gaul is divided into three parts, one of which the Belgae inhabit, the Aquitani another, those who in their own language are called Celts, in ours Gauls, the third."

The only confusion come with Masagetae tribe, who had the Getae name in it, but have iranic elements too (some rulers name, etc.). Most probably this was a mix betwen a Getae/Dacian tribe and a Scythian one. Similar views are for ex. about Cimbri and Teutoni, as being a Germano-Celtic mix, or Bastarnae (the same).

Let's not forget the Thyssagetae, who are really hard to pin down, but probably lived somewhere near the southern Ural Mountains.