Probably from giyach; the external abdomen, belly (as the source of the faetus (compare Giychown)) -- belly.
see HEBREW giyach
see HEBREW Giychown
H1512. gachon
גָּחוֺן noun masculine belly, of reptiles (compare perhaps Assyrian gi—innu, cord (from twisting ?) ZimBP 104) — גְּחֹנְךָ Genesis 3:14 (J) of the serpent, compare גָּחוֺן Leviticus 11:42 (P).
גחר (? compare Arabic retire, retreat, etc.)