“Put your hand under my thigh”
Place your hand under my thigh, and I will have you swear by the LORD, the God of heaven and the God of earth. (Genesis 24:2–3 BSB)
What it sounds like today
A bizarre and vaguely improper way to make someone promise something.
The cultural key
To modern ears the gesture is baffling, but it was a solemn oath-rite. The hand went near the loins, the seat of procreation and the place of the circumcision that marked the Abrahamic covenant. Swearing there tied the promise to one's descendants and to the covenant sign itself, making the oath as binding as one's own line. It appears again when the dying Jacob makes Joseph swear to bury him in Canaan (Genesis 47:29), always at moments concerning family, seed, and inheritance.
Recovered meaning
Abraham is not being crude; he is invoking the most binding oath he knows, sworn on the covenant marked in his own body. The servant's mission to find Isaac a wife is sealed by the very sign of the promise it serves.