Lewis & Short

transfŭgĭum, ii, n. [transfugio].

  1. I. Lit., a going over to the enemy, desertion (very rare): ut transfugia impeditiora essent, Liv. 22, 43, 5: crebra, ut in civili bello, Tac. H. 2, 34; 4, 70; id. A. 2, 46.
  2. II. Transf.: sacrarii, a migrating to Rome, Prud. adv. Symm. 2, 503: ad Christum de circumcisione, conversion, Sid. Ep. 8, 13.