transfuge

from The Collaborative International Dictionary of English v.0.48

Transfuge \Trans"fuge\, Transfugitive \Trans*fu"gi*tive\, n. [L.
   transfuga; trans across, over + fugere to flee.]
   One who flees from one side to another; hence, a deserter; a
   turncoat; an apostate. [R.]
   [1913 Webster]