late 12c., robben, "steal, take away (from someone) unlawfully; plunder or strip (a place) by force or violence," from Old French rober "rob, steal, pillage, ransack, rape," from West Germanic *rauba "booty" (source also of Old High German roubon "to rob," roub "spoil, plunder;" Old English reafian, source of the reave in bereave), from Proto-Germanic *raubon "to rob" (from PIE *runp- "to break;" see corrupt (adj.)).
Lord, hou schulde God approve þat þou robbe Petur, and gif þis robbere to Poule in þe name of Crist? [Wyclif, c. 1380]
To rob the cradle is attested from 1864 in reference to drafting young men in the American Civil War; by 1949 in reference to seductions or romantic relationships with younger persons. Related: Robbed; robbing.