crystalloid noun 2adjective 1forms 3 noun2 •Any substance that can be crystallized from solution; a water-soluble crystalline substance that can diffuse through a semipermeable membrane, as opposed to a colloid which cannot. •One of the microscopic particles resembling crystals, consisting of protein matter, which occur in certain plant cells. adjective1 •Crystal-like; transparent like crystal, or shaped like a crystal. formscrystalloids · more crystalloid · most crystalloid