Definition: (of a person) Subject to sudden or unpredictable changes
“With mercurial smile and incurable style she was only a dream.”
—“Broken” on The Process of Belief
In a sentence: Mitt Romney’s political beliefs are as mercurial as a baby’s moods.
Synonyms: fickle, capricious, temperamental, impulsive
Antonyms: staunch, dedicated, consistent, unchanging
sources: the google