not practicable; incapable of being put into practice with the available means

an impracticable plan.

unsuitable for practical use or purposes, as a device or material.

(of ground, places, etc.) impassable.

(of persons) hard to deal with because of stubbornness, stupidity, etc.

adjective

impractical , unattainable , unrealizable , unthinkable , unworkable , unnegotiable , unserviceable , unusable , useless , impossible , imprudent , infeasible , insuperable , unfeasible , unrealistic , unwise