Source : Webster's Revised Unabridged Dictionary (1913)

Primrose League \Prim"rose` League\ (Eng. Politics)
   A league of both sexes among the Conservatives, founded in
   1883. So called because primrose was (erroneously, it is
   said) taken to be the favorite flower of the Conservative
   statesman Benjamin Disraeli, Earl of Beaconsfield.