hiábavaló

• fool's errand

• piffle

• rope of sand

• rope of sand

• to plough the sands

• impertinence

• to flog a dead horse

• futilely, unavailingly, uselessly, vainly

• fillip, futility, idleness, piffle, vainness, vanity

• to waste one's labour

• to waste one's labour

• to make a waste of sg

• in mere waste