late 12c., from Old French rober "rob, steal, pillage, ransack, rape," from West Germanic *rauba "booty" (cf. 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 *reup-, *reub- "to snatch" (see rip (v.)).
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.
To harm one person in order to do good to another; by extension, to use money or resources set aside for one purpose for a different one.