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.
1640s, plural of datum, from Latin datum (thing) given, neuter past participle of dare to give (see date (n.1)). Meaning transmittable and storable computer information first recorded 1946. Data processing is from 1954.