Rashi on Deuteronomy 2:11/רש"י על דברים ב׳:י״א

1רפאים יחשבו וגו׳ THEY [ALSO] ARE ACCOUNTED REPHAIM, [AS THE ANAKIM] — As Rephaim are those Emim accounted, even as the Anakim — who are also termed Rephaim because the hands of everyone who beheld them became weak (רפה) (cf. Genesis Rabbah 26:7).

2אמים — so called because the dread (אימה) of them lay upon the people. — So, too, (v. 12) the Horim dwelt formerly in Seir and I gave them over unto the children of Esau. (Genesis Rabbah 26:7)