Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
fierce [fɪəs] adj (animal, person, look) свире́пый; (fighting) я́ростный; (loyalty) горя́чий*горя́ч (enemy, cold, hatred) лю́тый*лют (wind, heat, storm) стра́шный*стра́шен
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.
Русский: