The Oxford Thesaurus An A-Z Dictionary of Synonyms - impracticableadj.

1) unworkable, infeasible or unfeasible, impossible, unattainable, unachievable: The new engine design proved impracticable because of its high fuel consumption. 2) unsuitable, unfit, unusable, useless, inapplicable: As we have no electricity, air conditioners are impracticable.