late 14c., from rescue (v.). Earlier noun was rescous (early 14c.), from Old French rescous.
c. 1300, from stem of Old French rescorre "protect, keep safe; free, deliver" (Modern French recourre), from re-, intensive prefix (see re-), + escourre "to cast off, discharge," from Latin excutere "to shake off, drive away," from ex "out" (see ex-) + -cutere, combining form of quatere "to shake" (see quash). Related: Rescued; rescuing.