capricious
[adjective]
Synonyms: unpredictable, changeful, erratic, fickle, fitful, impulsive, inconsistent, inconstant, mercurial, variable, wayward, whimsical

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Antonyms: steadfast
Contrasted words: constant, steady
Related Words: humorsome, moody, effervescent

[TahlilGaran] English Synonym Dictionary ▲

ca‧pri‧cious /kəˈprɪʃəs/ adjective

1. likely to change your mind suddenly or behave in an unexpected way:
She was as capricious as her mother had been.

2. literary changing quickly and suddenly:
a capricious wind
—capriciously adverb

[TahlilGaran] Dictionary of Contemporary English ▲