Deuteronomy 2:11

Which also were accounted giants, as the Anakims ,.... Because of their bulky size and tall stature; or,"the Rephaim were they accounted, even they as the Anakims;'they were reckoned Rephaim, a name for giants in early times, even as the Anakims were; see Genesis 14:5 .

but the Moabites called them Emims ; to distinguish them from the Rephaim; so that it seems this name of Emims was not originally their name, but they are called so by a prolepsis, or anticipation, in Genesis 14:5 since they had it from the Moabites, a people of a later date.