The Collaborative International Dictionary of English v.0.48:

Therefore \There"fore\, conj. & adv. [OE. therfore. See There,
   and Fore, adv., For, and cf. Therefor.]
   1. For that or this reason, referring to something previously
      stated; for that.
      [1913 Webster]

            I have married a wife, and therefore I can not come.
                                                  --Luke xiv.
                                                  20.
      [1913 Webster]

            Behold, we have forsaken all, and followed thee;
            what shall we have therefore?         --Matt. xix.
                                                  27.
      [1913 Webster]

   2. Consequently; by consequence.
      [1913 Webster]

            He blushes; therefore he is guilty.   --Spectator.
      [1913 Webster]

   Syn: See Then.
        [1913 Webster]

WordNet (r) 3.0 (2006):

therefore
    adv 1: (used to introduce a logical conclusion) from that fact
           or reason or as a result; "therefore X must be true";
           "the eggs were fresh and hence satisfactory"; "we were
           young and thence optimistic"; "it is late and thus we
           must go"; "the witness is biased and so cannot be
           trusted" [syn: therefore, hence, thence, thus,
           so]
    2: as a consequence; "he had good reason to be grateful for the
       opportunities which they had made available to him and which
       consequently led to the good position he now held" [syn:
       consequently, therefore]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "therefore":
   according to circumstances, accordingly, after all,
   all things considered, and so, as a consequence, as a result,
   as it is, as matters stand, at that rate, because of that,
   because of this, before the bench, before the court,
   ceteris paribus, consequently, considering, equally, ergo,
   everything being equal, finally, for that, for that cause,
   for that reason, for this cause, for this reason, for which reason,
   hence, hereat, in court, in that case, in that event,
   inconsequence, inevitably, it follows that, naturally,
   naturellement, necessarily, of course, of necessity, on balance,
   on that account, on that ground, on the whole, on this account,
   propter hoc, so, sub judice, taking into account, that being so,
   then, thence, thereat, therefor, therefrom, thereupon,
   this being so, thus, thusly, thuswise, under the circumstances,
   whence, wherefore, wherefrom