1540s, "swelling, projecting and rounded, decorated with bosses" from boss (n.2). Meaning "domineering, fond of ordering people about" is recorded 1882, from boss (n.1) + -y (2). As a common cow name it represents Latin bos "cow" (see cow (n.)).
Domineering; autocratic: She's very bossy, a take-charge gal (1880s+)
[fr Latin bos, ''cow'']