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]