Viscous: The adjective form of “viscosity,” a property of a fluid that makes it resistant to deformation.
Honey is more viscous than water.
Vicious: cruel and/or violent. Wolves are vicious predators.
“Vicious circle” is a common expression describing a sequence of reciprocal adverse events that reinforce each other.
“Viscous circle” is a misspelling of “vicious circle.”