The Collaborative International Dictionary of English v.0.48:

Relevant \Rel"e*vant\ (-vant), a. [F. relevant, p. pr. of
   relever to raise again, to relieve. See Relieve.]
   1. Relieving; lending aid or support. [R.] --Pownall.
      [1913 Webster]

   2. Bearing upon, or properly applying to, the case in hand;
      pertinent; applicable.
      [1913 Webster]

            Close and relevant arguments have very little hold
            on the passions.                      --Sydney
                                                  Smith.
      [1913 Webster]

   3. (Scots Law) Sufficient to support the cause.
      [1913 Webster]

WordNet (r) 3.0 (2006):

relevant
    adj 1: having a bearing on or connection with the subject at
           issue; "the scientist corresponds with colleagues in
           order to learn about matters relevant to her own
           research" [ant: irrelevant]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "relevant":
   a propos, ad rem, adapted, admissible, akin, allied, allowable,
   appertaining, applicable, applying, apposite, appropriate, apropos,
   apt, associated, becoming, befitting, belonging, cognate,
   dovetailing, felicitous, fit, fitted, fitting, geared, germane,
   happy, important, in point, in question, involving, just right,
   likely, material, meshing, on the button, opportune, pat,
   pertaining, pertinent, proper, qualified, related, relative, right,
   seasonable, significant, sortable, suitable, suited, suiting,
   tailored, to the point, to the purpose, weighty