Antonyms of adj futile

2 senses of futile

Sense 1
futile, ineffectual, otiose, unavailing -- (producing no result or effect; "a futile effort"; "the therapy was ineffectual"; "an otiose undertaking"; "an unavailing attempt")

INDIRECT (VIA useless) -> useful, utile -- (being of use or service; "the girl felt motherly and useful"; "a useful job"; "a useful member of society")

Sense 2
bootless, fruitless, futile, sleeveless, vain -- (unproductive of success; "a fruitless search"; "futile years after her artistic peak"; "a sleeveless errand"; "a vain attempt")

INDIRECT (VIA unproductive) -> productive -- (producing or capable of producing (especially abundantly); "productive farmland"; "his productive years"; "a productive collaboration")

Similarity of adj futile

2 senses of futile

Sense 1
futile, ineffectual, otiose, unavailing -- (producing no result or effect; "a futile effort"; "the therapy was ineffectual"; "an otiose undertaking"; "an unavailing attempt")
       => useless (vs. useful) -- (having no beneficial use or incapable of functioning usefully; "a kitchen full of useless gadgets"; "she is useless in an emergency")

Sense 2
bootless, fruitless, futile, sleeveless, vain -- (unproductive of success; "a fruitless search"; "futile years after her artistic peak"; "a sleeveless errand"; "a vain attempt")
       => unproductive (vs. productive) -- (not producing or capable of producing; "elimination of high-cost or unproductive industries")