mercurial.

1. Quickly and unpredictably changing in mood, manner, or enthusiasm.

2. Containing or relating to the chemical element mercury.

Use it for

Words that belong together

• mercurial temperament
• mercurial moods

On the page

Her mercurial temperament kept the household guessing.

The director’s mercurial moods shaped each rehearsal.

Usage notes

Primary category: literary. Forms: Comparative more mercurial; superlative most mercurial in the personality sense. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.