Define viscous. viscous synonyms, viscous pronunciation, viscous translation, English dictionary definition of viscous. adj. 1. Having relatively high resistance to flow. 2. Viscid; sticky. vis′cous·ly adv. vis′cous·ness n. American Heritage® Dictionary of the English. Viscosity is the material property which relates the viscous stresses in a material to the rate of change of a deformation (the strain rate). Although it applies to general flows, it is easy to visualize and define in a simple shearing flow, such as a planar Couette flow. VISCOUS definition: 1. A viscous liquid is thick and sticky and does not flow easily. 2. A viscous liquid is thick and…. Learn more. VISCOUS definition: of a glutinous nature or consistency; sticky; thick; adhesive. See examples of viscous used in a sentence. VISCOUS meaning: 1. A viscous liquid is thick and sticky and does not flow easily. 2. A viscous liquid is thick and…. Learn more. Viscous means sticky, gluey and syrupy. So if something is viscous, you usually don't want to stick your fingers in it — that goes for boogers and maple syrup alike. viscous (comparative more viscous, superlative most viscous) Having a thick, sticky consistency between solid and liquid (that is, a high viscosity). Britannica Dictionary definition of VISCOUS [more viscous; most viscous] of a liquid : thick or sticky : not flowing easily viscous liquids A viscous fluid is any liquid or gas that resists flowing freely, caused by internal friction between its molecules as they move past each other. The higher the viscosity, the slower and thicker the fluid behaves. Honey is a classic example: pour it from a spoon and it moves sluggishly compared to water, which splashes and spreads almost instantly. That resistance you can see and feel is. The meaning of VISCOUS is having a thick or sticky consistency : viscid. How to use viscous in a sentence.