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early 15c., "action of manifesting; exhibition, demonstration," from Late Latin manifestationem (nominative manifestatio), noun of action from past participle stem of Latin manifestare (see manifest (adj.)). Meaning "an object, action, or presence by which something is made manifest" is from 1785. The spiritualism sense is attested from 1853.
manifestation man·i·fes·ta·tion (mān'ə-fě-stā'shən)
An indication of the existence, reality, or presence of something, especially an illness.