Mid 17th century (in an earlier sense). From post-classical Latin reservatorium storehouse from classical Latin reservāt-, past participial stem of reservāre + -ōrium.

Mid 17th century (in an earlier sense). From post-classical Latin reservatorius that may be used for keeping back or storage, reserved, set apart, of or belonging to reservation from classical Latin reservāt-, past participial stem of reservāre + -ōrius.