Viscosity is defined as a liquid’s resistance to flow. When the intermolecular forces of attraction are strong within a liquid, there is a larger viscosity. The opposite of viscosity is fluidity, which measures the ease of flow while liquids such as motor oil or honey, which are “sluggish” and high in viscosity, are known as viscous. Because part of a fluid moves, it forces other adjacent parts of the liquid to move along with it, causing an internal friction between the molecules, which ultimately leads to a reduced rate of flow.

Source: LibreTexts Chemistry