"overseer, one who employs or oversees workers," 1640s, American English, from Dutch baas "a master," Middle Dutch baes, a word of obscure origin. If the original sense was "uncle," perhaps it is related to Old High German basa "aunt," but some sources discount this theory.
The Dutch form baas is attested in English from 1620s as the standard title of a Dutch ship's captain. The word's popularity in U.S. may reflect egalitarian avoidance of master (n.) as well as the need to distinguish slave from free labor. The slang adjective meaning "excellent" is recorded in 1880s, revived, apparently independently, in teen and jazz slang in 1950s.
"protuberance, button," c. 1300, from Old French boce "a hump, swelling, tumor" (12c., Modern French bosse), from either Frankish *botija or Vulgar Latin *bottia, both of uncertain origin.
c. 1400, "to swell out; to beat or press into a raised ornament," from boss (n.2). From 1620s as "to furnish with bosses." Related: Bossed; bossing.
"be master or manager of, order and direct as a boss," 1856, from boss (n.1). Related: Bossed; bossing.
1540s, "swelling, projecting and rounded, decorated with bosses" from boss (n.2). The meaning "domineering, fond of ordering people about" is recorded by 1882, from boss (n.1) + -y (2). As a common cow name (by 1844) it represents Latin bos "cow" (from PIE root *gwou- "ox, bull, cow"). Related: Bossily; bossiness.
"boss of a shield," 1921, from Latin umbo "shield-boss, knob, projection."
"spiked metal ring for holding a belt, etc.," c. 1300, bukel, from Old French bocle "boss (of a shield)," then "shield," then by further extension "buckle, metal ring," (12c., Modern French boucle), from Latin buccula "cheek strap of a helmet," in Late Latin "boss of a shield," diminutive of bucca "cheek" (see bouche).
Boucle in the middle ages had the double sense of a "shield's boss" and "a ring"; the last sense has alone survived, and it metaph. developed in the boucle de cheveux, ringlets. [Kitchin]
"small, round shield used to ward off blows," c. 1300, from Old French bocler "boss (of a shield), shield, buckler" (12c., Modern French bouclier), from Medieval Latin *buccularius (adj.) "having a boss," from Latin buccula (see buckle (n.)).
especially in His Nibs "boss, employer, self-important person," 1821, of unknown origin; perhaps a variant of nob (n.2) "person of high position."