mercurial
Definitions
Subject to sudden or unpredictable changes of mood or mind.
Characterized by rapid and unpredictable changeableness of temperament.
Relating to or containing the element mercury.
Examples
The director's mercurial temperament made it difficult for the actors to know what to expect from one day to the next.
Despite his mercurial personality, he remained a brilliant and highly sought-after strategist in the tech industry.
Synonyms
volatile capricious fickle erratic unpredictable temperamental changeable
Antonyms
stable constant consistent steady reliable predictable immutable