14
useless(adjective, weak, sensible, inadequate, useful)
12
feeble(adjective, strong, fit, ineffective)
6
ineffective(adjective, strong, fit, useless, successful)
6
weak(adjective, inadequate, adequate)
6
dysfunctional(work, feature, state, adjective, function)
5
fruitless(adjective, weak, inadequate, fruitful)
5
time-consuming
4
ineffectual(adjective, useless, competent)
4
unorganized
4
worthless
3
abortive
3
empty(adjective, ineffective, fruitless)
3
feckless(adjective, purpose)
3
impotent(adjective, strong, weak, inadequate, competent)
3
incapable(adjective, strong, weak, fit, inadequate)
3
incompetent(adjective, strong, weak, inadequate, qualified)
3
inefficient(adjective, weak, sound, inadequate, competent)
3
inoperative
3
unproductive
3
sinful
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APASmart Define. (2015). effective thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/effective/thesaurus/antonyms
ChicagoSmart Define. 2015. "effective thesaurus" https://smartdefine.org/effective/thesaurus/antonyms (accessed September 20, 2026).
HarvardSmart Define 2015, effective thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/effective/thesaurus/antonyms>.
MLASmart Define. "effective thesaurus" 10 April 2015. Web. 20 September 2026. <https://smartdefine.org/effective/thesaurus/antonyms>