Antonyms of adj optimal

1 sense of optimal

Sense 1
optimum, optimal -- (most desirable possible under a restriction expressed or implied; "an optimum return on capital"; "optimal concentration of a drug")

INDIRECT (VIA best) -> worst -- ((superlative of `bad') most wanting in quality or value or condition; "the worst player on the team"; "the worst weather of the year")

Similarity of adj optimal

1 sense of optimal

Sense 1
optimum, optimal -- (most desirable possible under a restriction expressed or implied; "an optimum return on capital"; "optimal concentration of a drug")
       => best (vs. worst) -- ((superlative of `good') having the most positive qualities; "the best film of the year"; "the best solution"; "the best time for planting"; "wore his best suit")