The Collaborative International Dictionary of English v.0.48:

Boycott \Boy"cott`\, v. t. [imp. & p. p. Boycotted; p. pr. &
   vb. n. Boycotting.] [From Captain Boycott, a land agent in
   Mayo, Ireland, so treated in 1880.]
   To combine against (a landlord, tradesman, employer, or other
   person), to withhold social or business relations from him,
   and to deter others from holding such relations; to subject
   to a boycott.
   [1913 Webster]