- insoluble - (of a substance) not easily dissolved
Antonyms: soluble, dissolvable, dissoluble, meltable, disintegrable, water-soluble
- insoluble - admitting of no solution or explanation; "an insoluble doubt"
Antonyms: soluble, answerable, solvable, resolvable
- insoluble - without hope of solution; "an insoluble problem"
Antonym: hopeful (indirect, via hopeless)