The Collaborative International Dictionary of English v.0.48:

Phenomenal \Phe*nom"e*nal\, a. [Cf. F. ph['e]nom['e]nal.]
   Relating to, or of the nature of, a phenomenon; hence,
   extraordinary; wonderful; as, a phenomenal memory. --
   Phe*nom"e*nal*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

phenomenal
    adj 1: of or relating to a phenomenon; "phenomenal science"
    2: exceedingly or unbelievably great; "the bomb did fantastic
       damage"; "Samson is supposed to have had fantastic strength";
       "phenomenaRl feats of memory"

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "phenomenal":
   amazing, astonishing, astounding, beguiling, bewildering, bustling,
   corporeal, enigmatic, eventful, exceptional, extraordinary,
   fabulous, fantastic, fascinating, freakish, full of incident,
   gross, incomprehensible, inconceivable, incredible, indescribable,
   ineffable, legendary, marvelous, mind-blowing, mind-boggling,
   miraculous, momentous, mythical, noteworthy, objective, outlandish,
   outstanding, passing strange, physical, portentous, prodigious,
   puzzling, rare, remarkable, sensational, sensible, singular,
   staggering, stirring, strange, striking, stunning, stupefying,
   stupendous, substantial, tangible, unbelievable, uncommon,
   unexampled, unheard-of, unimaginable, unique, unorthodox,
   unparalleled, unprecedented, unspeakable, unthinkable, unusual,
   unwonted, wonderful, wondrous