Smith's Bible Dictionary

Zamzummim (Deuteronomy 2:20) only, the Ammonite name for the people who by others were called Rephaim. They are described as having originally been a powerful and numerous nation of giants. From a slight similarity between the two names, and from the mention of the Emim in connection with each, it is conjectured that the Zamzummim are identical with the Zuzim.