Antonyms of adj useful

2 senses of useful

Sense 1
useful (vs. useless), utile -- (being of use or service; "the girl felt motherly and useful"; "a useful job"; "a useful member of society")

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)

Sense 2
utilitarian, useful -- (having a useful function; "utilitarian steel tables")

INDIRECT (VIA functional) -> nonfunctional -- (not having or performing a function)

Similarity of adj useful

2 senses of useful

Sense 1
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)
          Also See-> effective#1, effectual#1, efficacious#2; expedient#1; helpful#1; profitable#1; serviceable#1

Sense 2
utilitarian, useful -- (having a useful function; "utilitarian steel tables")
       => functional (vs. nonfunctional) -- (designed for or capable of a particular function or use; "a style of writing in which every word is functional"; "functional architecture")