The Collaborative International Dictionary of English v.0.48:

Decided \De*cid"ed\, a.
   1. Free from ambiguity; unequivocal; unmistakable;
      unquestionable; clear; evident; as, a decided advantage.
      "A more decided taste for science." --Prescott.
      [1913 Webster]

   2. Free from doubt or wavering; determined; of fixed purpose;
      fully settled; positive; resolute; as, a decided opinion
      or purpose.

   Syn: Decided, Decisive.

   Usage: We call a thing decisive when it has the power or
          quality of deciding; as, a decisive battle; we speak
          of it as decided when it is so fully settled as to
          leave no room for doubt; as, a decided preference, a
          decided aversion. Hence, a decided victory is one
          about which there is no question; a decisive victory
          is one which ends the contest. Decisive is applied
          only to things; as, a decisive sentence, a decisive
          decree, a decisive judgment. Decided is applied
          equally to persons and things. Thus we speak of a man
          as decided in his whole of conduct; and as having a
          decided disgust, or a decided reluctance, to certain
          measures. "A politic caution, a guarded
          circumspection, were among the ruling principles of
          our forefathers in their most decided conduct."
          --Burke. "The sentences of superior judges are final,
          decisive, and irrevocable." --Blackstone.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decide \De*cide"\, v. t. [imp. & p. p. Decided; p. pr. & vb.
   n. Deciding.] [L. dec[imac]dere; de- + caedere to cut, cut
   off; prob. akin to E. shed, v.: cf. F. d['e]cider. Cf.
   Decision.]
   1. To cut off; to separate. [Obs.]
      [1913 Webster]

            Our seat denies us traffic here;
            The sea, too near, decides us from the rest.
                                                  --Fuller.
      [1913 Webster]

   2. To bring to a termination, as a question, controversy,
      struggle, by giving the victory to one side or party; to
      render judgment concerning; to determine; to settle.
      [1913 Webster]

            So shall thy judgment be; thyself hast decided it.
                                                  --1 Kings xx.
                                                  40.
      [1913 Webster]

            The quarrel toucheth none but us alone;
            Betwixt ourselves let us decide it then. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decided
    adj 1: recognizable; marked; "noticed a distinct improvement";
           "at a distinct (or decided) disadvantage" [syn:
           distinct, decided]

Moby Thesaurus II by Grady Ward, 1.0:

213 Moby Thesaurus words for "decided":
   SOL, absolute, accented, accentuated, adamant,
   admitting no exception, affirmative, affirmatory, all bets off,
   all off, all over, all up, all-out, arrant, arrogant, ascertained,
   assertative, assertional, assertive, assured, at an end, attested,
   bent, bound, bound and determined, canceled, categorical, certain,
   certified, classical, clear, clear-cut, cocksure, committed,
   complete, concluded, conclusive, confident, consummate, convinced,
   crass, dead, decisive, declarative, declaratory, dedicated,
   definite, definitive, defunct, deleted, determinate, determined,
   devoted, done, done for, done with, downright, earnest, egregious,
   emphasized, emphatic, ended, entire, established, evident,
   explicit, express, expunged, extinct, final, fini, finished, firm,
   fixed, flagrant, flat, flat-out, forceful, forcible, glaring,
   global, gross, guaranteed, hubristic, implicit, in red letters,
   in the bag, inappealable, incontestable, incontrovertible,
   indisputable, intent, intolerable, irrefutable, italicized, kaput,
   made sure, marked, nailed down, obstinate, obvious, on ice,
   open-and-shut, out-and-out, outright, over, overconfident,
   oversure, overweening, peremptory, perfect, perfected, persevering,
   persistent, persuaded, pointed, poised, pompous, positive,
   precious, predicational, predicative, profound, pronounced, proper,
   proud, proved, punctuated, purposeful, rank, reassured, regular,
   relentless, resolute, resolved, round, runaway, secure,
   self-assured, self-confident, self-important, self-reliant,
   serious, set, set at rest, settled, shattering, shocking, shot,
   sincere, single-minded, solid, stark, stark-staring, starred,
   stated, stony, straight, straight-out, stressed, superlative, sure,
   surpassing, tenacious, terminated, tested, the veriest, thorough,
   thoroughgoing, through, through with, total, tried, unafraid,
   unambiguous, unbearable, uncircumscribed, unconditional,
   unconditioned, unconscionable, undeniable, underlined, underscored,
   undisputed, undoubting, unequivocal, unfaltering, unhampered,
   unhesitating, unlimited, unmistakable, unmitigated, unqualified,
   unquestionable, unquestioned, unquestioning, unrelieved,
   unreserved, unrestricted, unspoiled, unswerving, unwaivable,
   unwavering, utter, warranted, washed up, whole, wholehearted,
   wiped out, without exception, without reserve, wound up, zapped