The Collaborative International Dictionary of English v.0.48:

Opportune \Op`por*tune"\, a. [F. opporiun, L. opportunus, lit.,
   at or before the port; ob (see Ob-) + a derivative of
   portus port, harbor. See Port harbor.]
   Convenient; ready; hence, seasonable; timely. --Milton.
   [1913 Webster]

         This is most opportune to our need.      --Shak.
   [1913 Webster] -- Op`por*tune"ly, adv. --
   Op`por*tune"ness, n.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Opportune \Op`por*tune"\, v. t.
   To suit. [Obs.] --Dr. Clerke(1637).
   [1913 Webster]

WordNet (r) 3.0 (2006):

opportune
    adj 1: suitable or at a time that is suitable or advantageous
           especially for a particular purpose; "an opportune place
           to make camp"; "an opportune arrival" [ant:
           inopportune]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "opportune":
   a propos, ad rem, adapted, advantageous, advisable, applicable,
   apposite, appropriate, apropos, apt, auspicious, becoming,
   befitting, beneficial, congruous, convenient, decent, desirable,
   dovetailing, expedient, favorable, feasible, felicitous, fit,
   fitted, fitten, fitting, fortunate, fructuous, geared, germane,
   good, happy, helpful, just right, likely, lucky, meet, meshing,
   on the button, pat, pertinent, politic, profitable, proper,
   propitious, prosperous, providential, qualified, recommendable,
   relevant, right, ripe, seasonable, seemly, sortable, suitable,
   suited, suiting, tailored, timely, to be desired, to the point,
   to the purpose, useful, well-timed, wise, worthwhile