The property of a material that is both viscous and elastic(noun)
The branch of rheology that studies such materials(noun)
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Use "viscoelasticity" in a sentence
"There are materials that have some limited flow known as viscoelasticity."
"Materials with viscoelasticity may seem to flow slowly for a while but then stop."
"Computations reveal that viscoelasticity alone does not give rise to a small, satellite bead between two much larger main beads but that inertia is required for its formation."