Shear thinning is a phenomenon where the viscosity of a material decreases as the rate of shear increases. It is a property observed in certain types of substances such as fluids, gels, and pastes. Some of the synonyms for shear thinning include pseudoplasticity, thixotropy, and rheopecty. Pseudoplasticity is a term used to describe the property of a material that has a decrease in viscosity as the shear rate increases, while thixotropy is a type of pseudoplasticity where the material appears to thicken or gel upon standing but will flow again when subjected to shear. Rheopecty is an opposite phenomenon and occurs when the viscosity of a material increases with increasing shear rate.