Plethora

According to the Oxford English Dictionary, the word plethora originated from the ancient Greek word plethein, meaning, to be full. This word stems from the Indo-Europeon root pele; to fill. The noun then passed into post-classical Latin and took the meaning, "fullness of habit" under its known name plethora. Those at www.oed.com speculate that the word came into its english usage through Middle French; plethore, in 1537, later to be used in Italian medicine with the word, pletora, and finally being adopted by the Portugese in 1601 as plethora.

The word is interesting in the sense that it has two different definitions;
In medicine, plethora orginally was defined as "an overabundance of one or more humours, especially blood". Its current medical use describes an excess of blood in the circulatory system or in a specific organ/area.

In everyday use, the word is used to depict an excess or superabundance.