mercurial
Mercurial (adjective) means Liable to sudden and unpredictable changes of mood or behaviour. Example: “His mercurial temper made him difficult to work for.”
How to use mercurial
Learner’s notesIn plain EnglishChanging mood or behaviour quickly and without warning.
Slightly literary; common in journalism, sports writing and profiles.
Do not confuse it with mercenary, which means motivated only by money.
Trace the full origin ↓Fill the gap
Can you complete this real example?
His _____ temper made him difficult to work for.
Etymology
From Latin mercurialis 'of Mercury', the Roman god of commerce and messages, whose swiftness gave the word its sense of quickness and changeability.