Definitions:

1. Refers to an unexpected or unpredictable change in behavior, action or situation. NOUN
   • The vagary of the weather made planning outdoor activities impossible.
2. Used to describe whims, eccentric ideas or sudden shifts that lack a clear cause or pattern. NOUN
   • The vagary of fate played a cruel hand in the tragic accident that clained his life.

Synonyms:

• caprice
• fancy
• impulse
• quirk
• whim