ETYM Cf. French viscosité, Late Lat. viscositas.
Resistance of a liquid to sheer forces (and hence to flow); SYN. viscousness.
The resistance of a fluid to flow when subjected to shear stress.
In physics, the resistance of a fluid to flow, caused by its internal friction, which makes it resist flowing past a solid surface or other layers of the fluid. It applies to the motion of an object moving through a fluid as well as the motion of a fluid passing by an object.
Fluids such as pitch, treacle, and heavy oils are highly viscous; for the purposes of calculation, many fluids in physics are considered to be perfect, or nonviscous.