somersault (n.)
1520s, from Middle French sombresault, from Old Provençal sobresaut, from sobre "over" (from Latin supra "over;" see supra-) + saut "a jump," from Latin saltus, from the root of salire "to leap" (see salient (adj.)). Sometimes further corrupted to somerset, etc.
somersault (v.)
1845, from somersault (n.). Related: Somersaulted; somersaulting.