plethorayoudaoicibaDictYouDict
plethora: [16] Greek plēthórē meant ‘fullness’ (it was derived from the verb pléthein ‘fill’, a descendant of the Indo-European base *plē-, from which English gets full, plenty, etc). It was taken over into late Latin as plēthōra, and at first was widely used as a medical term, denoting an ‘excess of blood or other fluids in the body’. That was what it originally denoted in English, but by the end of the 16th century the more general ‘surplus’ was coming into use.
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plethora (n.)youdaoicibaDictYouDict
1540s, a medical word for "excess of body fluid," from Late Latin plethora, from Greek plethore "fullness," from plethein "be full" (see pleio-). Figurative meaning "too-muchness, overfullness in any respect" is first recorded 1700. Related: Plethoric.