From H2909 (or H2902) in the sense of overlaying; (in the plural only) the kidneys (as being covered); hence (figuratively) the inmost thought: - inward parts.
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Gen 21:16And she went, and sat her down over against him a good way off, as it were a bowshotH2909: for she said, Let me not see the death of the child. And she sat over against him, and lift up her voice, and wept.