The Collaborative International Dictionary of English v.0.48:

Ripen \Rip"en\, v. i. [imp. & p. p. Ripened;p. pr. & vb. n.
   Ripening.]
   1. To grow ripe; to become mature, as grain, fruit, flowers,
      and the like; as, grapes ripen in the sun.
      [1913 Webster]

   2. To approach or come to perfection.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ripening
    n 1: coming to full development; becoming mature [syn:
         maturation, ripening, maturement]
    2: acquiring desirable qualities by being left undisturbed for
       some time [syn: ripening, aging, ageing]