bully (v.) Look up bully at Dictionary.com
1710, from bully (n.). Related: Bullied; bullying.
bully (n.) Look up bully at Dictionary.com
1530s, originally "sweetheart," applied to either sex, from Dutch boel "lover; brother," probably a diminutive of Middle Dutch broeder "brother" (compare Middle High German buole "brother," source of German Buhle "lover;" see brother (n.)).

Meaning deteriorated 17c. through "fine fellow" and "blusterer" to "harasser of the weak" (1680s, from bully-ruffian, 1650s). Perhaps this was by influence of bull (n.1), but a connecting sense between "lover" and "ruffian" may be in "protector of a prostitute," which was one sense of bully (though not specifically attested until 1706). "Sweetheart" words often go bad in this way; compare leman, also ladybird, which in Farmer & Henley is "1. A whore; and (2) a term of endearment." The expression meaning "worthy, jolly, admirable" (especially in 1864 U.S. slang bully for you!) is first attested 1680s, and preserves an earlier, positive sense of the word.