Source : Webster's Revised Unabridged Dictionary (1913)

Vicissitude \Vi*cis"si*tude\, n. [L. vicissitudo, fr. vicis
   change, turn: cf. F. vicissitude. See {Vicarious}.]
   1. Regular change or succession from one thing to another;
      alternation; mutual succession; interchange.

            God made two great lights . . . To illuminate the
            earth and rule the day In their vicissitude, and
            rule the night.                       --Milton.

   2. Irregular change; revolution; mutation.

            This man had, after many vicissitudes of fortune,
            sunk at last into abject and hopeless poverty.
                                                  --Macaulay.

Source : WordNet®

vicissitude
     n 1: a variation in circumstances or fortune at different times
          in your life or in the development of something; "the
          project was subject to the usual vicissitudes of
          exploratory research"
     2: mutability in life or nature (especially successive
        alternation from one condition to another)