Antonyms of adj useless

1 sense of useless

Sense 1
useless (vs. useful) -- (having no beneficial use or incapable of functioning usefully; "a kitchen full of useless gadgets"; "she is useless in an emergency")

useful (vs. useless), utile -- (being of use or service; "the girl felt motherly and useful"; "a useful job"; "a useful member of society")
        => multipurpose -- (having multiple uses; "a multipurpose tool")
        => reclaimable, recyclable, reusable -- (capable of being used again)
        => serviceable -- (capable of being put to good use; "a serviceable kitchen gadget")
        => useable, usable -- (capable of being put to use; "usable byproducts")
        => utilitarian -- (having utility often to the exclusion of values; "plain utilitarian kitchenware")
        => utilizable -- (capable of being put to a profitable or practical use)

Similarity of adj useless

1 sense of useless

Sense 1
useless (vs. useful) -- (having no beneficial use or incapable of functioning usefully; "a kitchen full of useless gadgets"; "she is useless in an emergency")
       => futile, ineffectual, otiose, unavailing -- (producing no result or effect; "a futile effort"; "the therapy was ineffectual"; "an otiose undertaking"; "an unavailing attempt")
       => inutile -- (not worth using)
       => unserviceable, unusable, unuseable -- (not capable of being used)
          Also See-> ineffective#1, uneffective#1, ineffectual#1; unprofitable#1; unserviceable#1