Dialysis /(?)/ Di·al·y·sis Dialysis n. pl. Dialyses Diæresis. See Diæresis, 1. (Gram.) Same as Asyndeton. (Rhet.) Debility. (Med.) The separation of different substances in solution, as crystalloids and colloids, by means of their unequal diffusion, especially through natural or artificial membranes. (Chem.)