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1560s, from Late Latin emanationem (nominative emanatio), noun of action from past participle stem of Latin emanare "flow out, arise, proceed," from ex- "out" (see ex-) + manare "to flow," from PIE root *ma- "damp."
emanation em·a·na·tion (ěm'ə-nā'shən)
Something that issues from a source; an emission.
Any of several radioactive gases that are isotopes of radon and are products of radioactive decay.