Origin: 1350–1400;Middle Englishreteinen < Old Frenchretenir < Latinretinēre to hold back, hold fast, equivalent to re-re- + -tinēre, combining form of tenēre to hold
late 14c., from O.Fr. retenir, from L. retinere "hold back," from re- "back" + 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.