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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.