The Collaborative International Dictionary of English v.0.48:

Vagary \Va*ga"ry\ (v[.a]*g[=a]"r[y^] or v[a^]g"[.a]*r[-e]), n.;
   pl. Vagaries (v[.a]*g[=a]"r[i^]z or v[a^]g"[.a]*r[-e]z).
   [L. vagari to stroll about. See Vague.]
   [1913 Webster]
   1. A wandering or strolling. [Obs.]
      [1913 Webster]

   2. Hence, a wandering of the thoughts; a wild or fanciful
      freak; a whim; a whimsical purpose. "The vagaries of a
      child." --Spectator.
      [1913 Webster]

            They changed their minds,
            Flew off, and into strange vagaries fell. --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vagary
    n 1: an unexpected and inexplicable change in something (in a
         situation or a person's behavior, etc.); "the vagaries of
         the weather"; "his wealth fluctuates with the vagaries of
         the stock market"; "he has dealt with human vagaries for
         many years"

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "vagary":
   aberration, bee, boutade, brainstorm, capriccio, caprice,
   circuitousness, conceit, crank, craze, crazy idea, crosswiseness,
   crotchet, daydream, declination, deflection, deflexure, deviance,
   deviation, deviousness, diagonality, digression, divagation,
   divergence, dream, excursion, fad, fancy, fantastic notion,
   fantasy, flimflam, fool notion, freak, freakish inspiration,
   harebrained idea, humor, indirection, indirectness, kink, maggot,
   megrim, nonconformity, notion, obliqueness, obliquity,
   passing fancy, quirk, skewness, squint, toy, transverseness, whim,
   whim-wham, whimsy