1896, Amer.Eng. from feistsmall dog,” from fice, fist Amer.Eng. 1805 “small dog,” short for fysting curre “stinking cur,” attested from 1529, from M.E. fysten, fisten “break wind” (1440), related to O.E. fisting “stink.” The 1811 slang dictionary defines fice as “a small windy escape backwards, more obvious to the nose than ears; frequently by old ladies charged on their lap-dogs.” Cf. also Dan. fise “to blow, to fart,” and obs. Eng. askefise, lit. “fire-blower, ash-blower,” from an unrecorded O.N. source, used in M.E. for a kind of bellows, but orig. “a term of reproach among northern nations for an unwarlike fellow who stayed at home in the chimney corner” [O.E.D.]

From http://dictionary.reference.com/browse/feisty