Some common synonyms of fickle are capricious, inconstant, mercurial, and unstable. While all these words mean "lacking firmness or steadiness (as in purpose or devotion)," fickle suggests unreliability because of perverse changeability and incapacity for steadfastness.

// performers discover how fickle fans can be

The meanings of inconstant and fickle largely overlap; however, inconstant implies an incapacity for steadiness and an inherent tendency to change.

// an inconstant friend

In some situations, the words capricious and fickle are roughly equivalent. However, capricious suggests motivation by sudden whim or fancy and stresses unpredictability.

// an utterly capricious critic