The act of entombing or the state of being entombed(noun)
The decommissioning of a radioactive site by encasing it in concrete(noun)
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Use "entombment" in a sentence
"Another option is "entombment" of radioactive components in concrete for the long term."
"When Mr. Bounderby in "Hard Times," for example, tells stories about his supposed childhood poverty, he brags that as a boy the only pictures he possessed were "of a man shaving himself in a boot on the blacking bottles"—a brisk little nod to Dickens's youthful entombment at Mr. Warren's factory in the Strand."
"It signified her participation in the entombment of"