Synonyms for Futile (same or very similar meaning)
WordNet sense 1 (producing no result or effect):
ineffectual, otiose, unavailingWordNet sense 2 (having no beneficial use or incapable of functioning usefully):
uselessWordNet sense 3 (unproductive of success):
bootless, fruitless, sleeveless, vainFrom the ODE community, based on WordNetadd/edit