Impracticable

abstract absurd chimerical idealistic illogical impossible impracticable improbable inapplicable inefficacious infeasible inoperable irrealizable ivory-tower no-go nonfunctional nonviable not a prayer otherworldly out of the question quixotic romantic speculative starry-eyed theoretical unattainable unbusinesslike unfeasible unreal unserviceable unusable unwise unworkable useless visionary wild won’t fly