When you hear the word viscous, imagine something thick, sticky, and slow-moving. It’s a descriptive adjective that reveals how fluids or substances behave. Unlike water, which flows easily, viscous substances resist flow; they’re sticky and slimy. 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. / ˈvɪs·kəs / (of a liquid) thick and sticky; not flowing easily: viscous oil (Definition of viscous from the Cambridge Academic Content Dictionary © Cambridge University Press) / ˈvɪs·kəs / (of a liquid) thick and sticky; not flowing easily: viscous oil (Definition of viscous from the Cambridge Academic Content Dictionary © Cambridge University Press) 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. Not quite a solid and not quite a liquid, scientists like to say that viscous things don't flow very easily. 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. Define viscous. viscous synonyms, viscous pronunciation, viscous translation, English dictionary definition of viscous. adj. 1. Having relatively high resistance to flow. Adjective viscous (comparative more viscous, superlative most viscous) Having a thick, sticky consistency between solid and liquid (that is, a high viscosity). Synonyms: syrupy, viscid, viscose, thickflowing Antonym: inviscid The meaning of VISCOUS is having a thick or sticky consistency : viscid. How to use viscous in a sentence. 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. Not quite a solid and not quite a liquid, scientists like to say that viscous things don't flow very easily.