fickle
adj.adj. changing your mind or feelings very often and without a good reason. You use this to describe someone who is not loyal or something that is not reliable.
adj. characterised by erratic changeability in affections, interests, or loyalties. Often used to describe weather patterns, public opinion, or personal commitment.
The weather here is very fickle.
Success in the fashion industry is difficult because consumer tastes are notoriously fickle and change every season.
Politicians often struggle to maintain high approval ratings among a fickle electorate that quickly forgets past achievements when faced with immediate economic challenges.
From Middle English fikil, fikel, from Old English ficol (“fickle, cunning, tricky, deceitful”), equivalent to fike + -le. More at fike.
From Middle English fikelen, from fikel (“fickle”); see above. Cognate with Low German fikkelen (“to deceive, flatter”), German ficklen, ficheln (“to deceive, flatter”).
Typically used as a predicative adjective after 'be' or 'become', or attributively before nouns like 'nature', 'weather', or 'fan'.