Know how to use "fewer" and "less"? Find out.
late 14c., "hold back, restrain;" c.1400, "continue keeping, keep possession of," from Old French retenir "keep, retain; take into feudal service; hold back; remember" (12c.), from Latin retinere "hold back, keep back, detain, restrain," from re- "back" (see re-) + tenere "to hold" (see tenet). Meaning "keep (another) attached to one's person, keep in service" is from mid-15c.; specifically of lawyers from 1540s. Meaning "keep in the mind" is from c.1500. Related: Retained; retaining.