The Collaborative International Dictionary of English v.0.48:

Maniacal \Ma*ni"a*cal\, a.
   Affected with, or characterized by, madness; maniac. --
   Ma*ni"a*cal*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

maniacal
    adj 1: wildly disordered; "a maniacal frenzy" [syn: maniacal,
           maniac(p)]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "maniacal":
   Dionysiac, abandoned, amok, bacchic, bellowing, berserk,
   carried away, corybantic, crazy, delirious, demented, demoniac,
   deranged, desperate, distracted, ecstatic, enraptured, feral,
   ferocious, fierce, frantic, frenetic, frenzied, fulminating,
   furious, haggard, hog-wild, howling, hysterical, in a transport,
   in hysterics, insane, intoxicated, like one possessed, loony,
   lunatic, mad, madding, maenadic, maniac, manic, mentally ill,
   non compos mentis, of unsound mind, orgasmic, orgiastic, possessed,
   psychotic, rabid, raging, ramping, ranting, raving, raving mad,
   ravished, roaring, running mad, running wild, stark-raving mad,
   storming, transported, uncontrollable, violent, wild, wild-eyed,
   wild-looking