From the same as 'eben; a pair of stones (only dual); a potter's wheel or a midwife's stool (consisting alike of two horizontal disks with a support between) -- wheel, stool.
KJV: And he said, When ye do the office of a midwife to the Hebrew women, and see them upon the stools; if it be a son, then ye shall kill him: but if it be a daughter, then she shall live.
NASB: and he said, "When you are helping the Hebrew women to give birth and see them upon the birthstool, if it is a son, then you shall put him to death; but if it is a daughter, then she shall live."