Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

fanatical
     adj : marked by excessive enthusiasm for and intense devotion to a
           cause or idea; "rabid isolationist" [syn: {fanatic}, {overzealous},
            {rabid}]