1540s, "a sudden rush, dash, or springing forth; specifically of troops from a besieged place, attacking the besiegers," from French saillie "a rushing forth," noun use of fem. past participle of saillir "to leap," from Latin salire "to leap" (see salient (adj.)). Sally-port "gate or passage in a fortification to afford free egress to troops in making a sally" is from 1640s.
