Source : Webster's Revised Unabridged Dictionary (1913)

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.

         This is most opportune to our need.      --Shak.
   -- {Op`por*tune"ly}, adv. -- {Op`por*tune"ness}, n.

Source : WordNet®

opportuneness
     n : timely convenience [syn: {patness}, {timeliness}] [ant: {inopportuneness}]