Antonyms of adj high-grade

1 sense of high-grade

Sense 1
high-grade, top-quality, top-grade -- (surpassing in quality; "top-grade ore")

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 high-grade

1 sense of high-grade

Sense 1
high-grade, top-quality, top-grade -- (surpassing in quality; "top-grade ore")
       => 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")