1560, "blustering, swaggering fighting man" (earlier simply swash, 1549), from swash "fall of a blow" (see swash) + buckler "shield." The original sense seems to have been "one who makes menacing noises by striking his or an opponent's shield." Swashbuckling (adj.) is attested from 1693.
[swosh-buhk-ler, swawsh-] 
lər