adjective

(of a task or undertaking) ineffectual; useless.

remonstrating with him seems ever to have been a bootless task

useless,ineffective,ineffectual,inefficacious,unproductive,fruitless,profitless,unrewarding,unsuccessful,non-successful,without success,abortive,unavailing,to no avail,to no effect,to no purpose,futile,vain,in vain,pointless,worthless,nugatory,a dead loss,Sisyphean,for nought,unfructuous