1)
What is the meaning of "Tero'em"?
1.
Rashi: You will crush them.
2.
Radak: You will break them. This is like "ha'Yaro'a Barzel" (Yirmeyah 15:12), "Yaro'a Kabirim" (Iyov 34:24).
2)
What is "Shevet Barzel"?
1.
Rashi: It is the sword.
3)
What is the meaning of "Tenapetzem "?
1.
Rashi: You will break them. In all of Tanach, Niputz is destruction into small pieces. Malbim - David was authorized to totally destroy other nations.
2.
Radak: You will break and scatter them. One who breaks an earthenware Kli, the shards scatter. The same applies to "v'Nafotz ha'Kadim" (Shoftim 7:19).