Viscous means, according to https://www.thefreedictionary.com/viscous
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Having relatively high resistance to flow.
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Viscid; sticky.
Vicious means, from https://www.thefreedictionary.com/vicious
vi·cious (vĭsh′əs)
adj.
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Mean-spirited or deliberately hurtful; malicious: vicious gossip.
2.
a. Extremely violent or injurious; cruel: a vicious blow to the stomach; vicious tactics in suppressing a rebellion.
b. Marked by an aggressive disposition. Used chiefly of animals.
c. Disposed to violent or destructive behavior: a vicious dictator.
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Severe, powerful, or intense; fierce: a vicious storm.
4.
a. Having the nature of vice; evil, immoral, or depraved: "All men who succeed … in finance in New York at last … return to their native towns, assert that cities are vicious, marry their childhood sweethearts" (Sinclair Lewis).
b. Given to vice, immorality, or depravity: "The sum and substance of it was, That Oliver was a foundling, born of low and vicious parents" (Charles Dickens).
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Faulty or defective: a forced, vicious style of prose.