unrealistic
definition
not having a basis in reality or truth
example
Many people have unrealistic expectations about how quickly they can achieve their career goals.
synonyms
impracticalunattainablefanciful
word origin — The word 'unrealistic' is formed by adding the prefix 'un-' meaning 'not' to 'realistic', which derives from 'realism' based on the Latin 'realis' meaning 'actual' or 'true'.