The Collaborative International Dictionary of English v.0.48:
Fanatical \Fa*nat"ic*al\, a. Characteristic of, or relating to, fanaticism; fanatic. -Fa*nat"ic*al*ly, adv. -- Fa*nat"ic*al*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
fanatically adv 1: in a passionately fanatic manner; "he followed the teachings of his guru fanatically"