BILHAH
(bil' hah) HEBREW: BILHA
possibly "simplicity" or "modesty"
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When Rachel was unable to conceive a child, she sent her maid Bilhah to Jacob as a surrogate for herself. Bilhah's sons by Jacob were Dan and Naphtali. Their names were given them not by Bilhah but by Rachel, who had authority over them as if they were her own children. Much later, Jacob's eldest son Reuben committed adultery with Bilhah.
{E2 Dictionary of Biblical People}