Jacob's thigh was disabled by the Angel, to show the patriarch that his prevalence was through his faith and prayer, not through force, Genesis 32:25-31. Smiting the thigh was a gesture of self-condemnation and grief, Jeremiah 31:19 Ezekiel 21:12.
In general, a datum is a base elevation used as a reference from which to reckon heights or depths. A tidal datum is a standard elevation defined by a certain phase of the tide.
Related to datum: datum line. , pl. (dÄ'tÅ­m, dÄ'tÄ), A piece of information acquired by observation, measurement, or experiment and used as a basis for calculation or inference. See: data. [L., given, fr. do, pp. datum, to give] See data.