Rephaim

lofty men; giants, [(Gen 14:5; 2Sam 21:16 ; 21:18), marg. A.V., Rapha, marg. R.V., Raphah; (Deut 3:13), R.V.; A.V., "giants"]. The aborigines of Palestine, afterwards conquered and dispossessed by the Canaanite tribes, are classed under this general title. They were known to the Moabites as Emim, i.e., "fearful", (Deut 2:11), and to the Ammonites as Zamzummim. Some of them found refuge among the Philistines, and were still existing in the days of David. We know nothing of their origin. They were not necessarily connected with the "giants" (R.V., "Nephilim") of (Gen 6:4). (See GIANTS)

EBD - Easton's Bible Dictionary