The Collaborative International Dictionary of English v.0.48:

Vicissitude \Vi*cis"si*tude\, n. [L. vicissitudo, fr. vicis
   change, turn: cf. F. vicissitude. See Vicarious.]
   [1913 Webster]
   1. Regular change or succession from one thing to another;
      alternation; mutual succession; interchange.
      [1913 Webster]

            God made two great lights . . .
            To illuminate the earth and rule the day
            In their vicissitude, and rule the night. --Milton.
      [1913 Webster]

   2. Irregular change; revolution; mutation.
      [1913 Webster]

   3. (pl.) Changing conditions of fortune in one's life; life's
      ups and downs.
      [PJC]

            This man had, after many vicissitudes of fortune,
            sunk at last into abject and hopeless poverty.
                                                  --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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)

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "vicissitude":
   adverse circumstances, adversity, affliction, aggravation,
   alteration, alternation, annoyance, asperity, blight, bummer, care,
   chain of circumstances, chain reaction, change, changeability,
   changes, chapter of accidents, chop and change,
   concatenation of events, contrasts, cross, curse, difficulties,
   difficulty, diversity, downer, feast and famine, fluctuation,
   flukiness, flux, hard knocks, hard life, hard lot, hardcase,
   hardness, hardship, inconstancy, innovation, ins and outs,
   irritation, mischance, misfortune, mutability, mutation, novelty,
   oscillation, pendulation, permutation, plight, predicament,
   pressure, progression, reversal, rigor, sea of troubles, seesawing,
   shifting, shuffling, sport, stress, stress of life,
   teeter-tottering, teetering, tottering, transposition, trial,
   tribulation, trouble, troubles, unpredictability, ups and downs,
   vacillation, vale of tears, variability, variation, variations,
   variety, vicious circle, vicissitudes, vicissitudes of fortune,
   wavering