Friction is due to resistance between two solid surfaces where viscosity is due to cohesion or adhesion between two liquid surfaces.
Viscosity is defined as a measure of the resistance of a fluid, which is being deformed by either shear stress or tensile stress. In more common words, viscosity is the internal friction of a fluid. Its also referred as the thickness of a fluid. Viscosity is simply the friction between two layers of a fluid when the two layers move relative to each other
Friction is caused by the contact of two rough surfaces. Friction has five modes; dry friction that occurs between two solid bodies, fluid friction, which is also known as viscosity, lubricated friction, where two solids are separated by a liquid layer, skin friction, which opposes a moving solid in a liquid, and internal friction that causes the internal components of a solid to make friction.