(n.) Drilling Fluids. A unit of measurement for viscosity equivalent to one-hundredth of a poise and symbolized by cP. Viscosity is the ratio ofshear stress to shear rate, giving the traditional unit of dyne-sec/cm2 for Poise. In metric (SI) units, one cP is one millipascal-second. See: apparent viscosity, poise, power-law fluid, rheology