insoluble UK /ɪnˈsɒljʊbəl/US /ɪnˈsɑljəbəl/adjective 4noun 1forms 3 adjective4 •That cannot be dissolved.Petroleum is largely insoluble in water. •That cannot be broken down or dispersed. •That cannot be solved.This dispute, as already stated was insoluble in the ideological context in which it took place. — 1978 •That cannot be explained. noun1 •Any substance that cannot be dissolved.As there is a partial vacuum inside the drum, the liquid is sucked inside the drum and the insolubles are deposited on the outer surface of the membrane filter. — 2006 formsinsolubles · more insoluble · most insoluble