The Collaborative International Dictionary of English v.0.48:

Exceptional \Ex*cep"tion*al\, a. [Cf. F. exceptionnel.]
   Forming an exception; not ordinary; uncommon; rare; hence,
   better than the average; superior. --Lyell.
   [1913 Webster]

         This particular spot had exceptional advantages.
                                                  --Jowett (Th.
                                                  )
   -- Ex*cep"tion*al*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

exceptional
    adj 1: far beyond what is usual in magnitude or degree; "a night
           of exceeding darkness"; "an exceptional memory";
           "olympian efforts to save the city from bankruptcy"; "the
           young Mozart's prodigious talents" [syn: exceeding,
           exceptional, olympian, prodigious, surpassing]
    2: surpassing what is common or usual or expected; "he paid
       especial attention to her"; "exceptional kindness"; "a matter
       of particular and unusual importance"; "a special occasion";
       "a special reason to confide in her"; "what's so special
       about the year 2000?" [syn: especial(a), exceptional,
       particular(a), special]
    3: deviating widely from a norm of physical or mental ability;
       used especially of children below normal in intelligence;
       "special educational provisions for exceptional children"

Moby Thesaurus II by Grady Ward, 1.0:

163 Moby Thesaurus words for "exceptional":
   aberrant, abnormal, absolute, anomalous, appalling, astonishing,
   beguiling, bewildering, celebrated, certain, concrete, conspicuous,
   crank, crankish, cranky, crotchety, deficient, defined, definite,
   detailed, determinate, deviant, deviative, different, distinct,
   distinguished, divergent, dotty, eccentric, egregious, eminent,
   enigmatic, erratic, esoteric, especial, esteemed, estimable,
   ethnocentric, excellent, excluding, exclusive, exclusory, express,
   extraordinary, fabulous, fantastic, fascinating, fey, fixed, flaky,
   formidable, freakish, funny, gifted, good, handicapped, idiocratic,
   idiosyncratic, inadmissible, incomprehensible, inconceivable,
   incredible, indescribable, individual, ineffable, infrequent,
   inner, insular, intimate, irregular, kinky, kooky, legendary,
   maggoty, marked, marvelous, memorable, minute, miraculous,
   mythical, narrow, noble, notable, noteworthy, noticeable, nutty,
   odd, oddball, of mark, outlandish, outstanding, parochial,
   particular, passing strange, peculiar, personal, phenomenal,
   portentous, precise, preclusive, premium, prescriptive,
   prestigious, preventive, private, prodigious, prohibitive,
   prominent, puzzling, queer, quirky, rare, remarkable, rememberable,
   reputable, respective, restrictive, salient, scarce, screwball,
   screwy, seclusive, segregative, select, selective, sensational,
   separative, several, signal, singular, snobbish, solipsistic,
   special, specific, strange, striking, stupefying, stupendous,
   superior, talented, telling, twisted, uncommon, unconventional,
   uncustomary, unexampled, unforgettable, unheard-of, unimaginable,
   unique, unnatural, unordinary, unparalleled, unprecedented,
   unspeakable, unthinkable, unusual, unwonted, wacky, whimsical,
   wonderful, wondrous, xenophobic