unrealistic
adj. B1 Intermediate US //ənˌɹiˈɫɪstɪk// UK //ʌnɹiəlˈɪstɪk// un·re·al·is·tic
adj. not based on what is real or possible. You use this when a plan or idea is too difficult to achieve.
adj. not in accordance with reality or practical possibility; lacking a basis in fact or feasible conditions.
His plan to finish the book in one day is unrealistic.
The manager called the sales target unrealistic because the market had shrunk.
Critics argued that the proposal was unrealistic, ignoring the severe budget constraints and logistical hurdles involved.
From un- + realistic.