Resembling a crystal.n. The name given by Professor Graham to a class of bodies which have the power, when in solution, of passing easily through membranes, as parchment-paper, and which he found to be of a crystalline character.n. A protein crystal—that is, a granule of protein in the form of a crystal, differing from an organic crystal in the inconstancy of its angles and in its property of swelling when immersed in water. Such crystalloids are of various forms and usually colorless.