late 14c., from Old French escarmouche "skirmish," from Italian scaramuccia, earlier schermugio, probably from a Germanic source (compare Old High German skirmen "to protect, defend"), with a diminutive or depreciatory suffix, from Proto-Germanic *skerm-, from PIE root *sker- (1) "to cut."
Influenced in Middle English by a separate verb skirmysshen "to brandish a weapon," from Old French eskirmiss-, stem of eskirmir "to fence," from Frankish *skirmjan, from the same Germanic source. Compare scrimmage. Other modern Germanic forms have an additional diminutive affix: German scharmützel, Dutch schermutseling, Danish skjærmydsel. Skirmish-line attested by 1864.