See J.N. Ford, "Three Hapax Legomena in the Babylonian Talmud", Le Muséon 130 (1-2), pp. 1-30 where, citing S. Shaked, an Iranian etymology is proposed; however, we prefer the etymology from the root gdm as proposed by M. Morgenstern in JSS 52(2007): 257, as clearly indicated in the scribal "correction" in the cited magic bowl passage.