IPA: /ˌʌn.rɪəˈlɪs.tɪk/
KK: /ʌnˈrɪəˌlɪstɪk/
Not based on reality; too idealistic or impractical to be true or achievable.
Her plans for a perfect world are simply unrealistic.
Unrealistic → It is formed from "un-" (meaning not) and "realistic" (from "real" which comes from Latin "realis", meaning actual or true, and the suffix "-istic" which indicates a characteristic). The word "unrealistic" means not having the characteristics of reality or practicality.
Think of 'not' ('un-') being added to 'real' ('realis') to remember that 'unrealistic' describes something that is not true or practical.