the knee: the joint in the middle of the leg, and the shelf a seated person's knees make
This is the ordinary word for the knee, and it never stops being that. What gives it range is what the joint does. The knees are what hold a person upright and let them walk, run, and keep going, so they became a natural way to speak about someone's strength and about the moment that strength gives out.
That one fact produces two opposite pictures. Knees that shake, buckle, or will not hold are the body confessing terror or exhaustion. Knees bent on purpose are the reverse: a person lowering their own height in front of someone greater, which is why kneeling became the standard posture of prayer and of loyalty, and why "every knee shall bow" could stand for the whole world acknowledging God.
A seated person's knees also make a shelf, so this is where a baby is delivered onto, received, held, and bounced. Several of those scenes are argued over: readers have long asked whether setting a newborn on someone's knees was a recognized way of claiming the child for a family or simply a gesture of welcome. The word itself settles nothing either way. It stays close to the bosom (חֵיק), the fold against the chest where a child is carried and nursed, while naming the lower, outward shelf instead.
Greek translators used one plain word for knee throughout (γόνυ), and the New Testament picked up the line about every knee bowing straight from this word's most famous verse.
Nuances
Whether bearing a child "on the knees" in Genesis 30:3 is a formal legal act of adoption or legitimation, or an informal gesture.
- contestedA recognized symbolic legal act: placing the newborn on the knees establishes the claim to the child, with parallels in Hurrian, Hittite, and Mesopotamian material.; E. A. Speiser, Genesis, Anchor Bible 1 (Garden City, NY: Doubleday, 1964), at Gen 30:3; Nahum M. Sarna, Genesis, JPS Torah Commentary (Philadelphia: Jewish Publication Society, 1989), at Gen 30:3; Meir Malul, "Adoption of Foundlings in the Bible and Mesopotamian Documents," JSOT 46 (1990): 97-126
- contestedNo ceremony is in view: cross-cultural parallels place a newborn on the knees of a natural parent or grandparent, the one clear biblical adoption is done by spoken declaration, and the handmaid's child already belongs to the wife who owns her.; Jeffrey H. Tigay, "Adoption," Encyclopaedia Judaica, 2nd ed. (Detroit: Macmillan Reference, 2007), 1:415-420; Frederick E. Greenspahn, When Brothers Dwell Together: The Preeminence of Younger Siblings in the Hebrew Bible (New York: Oxford University Press, 1994); Ephraim Landau, "Giving Birth on Someone's Knees/Lap," Jewish Bible Quarterly 48:4 (2020)