plethora

Plethora is a noun meaning an excessive or more than adequate amount of something; it can refer to abundance as well as excess. The term comes from the Greek plethoreia, from plethyssein "to be full," and entered English in the late Renaissance. In ordinary usage it denotes a large quantity, sometimes with the connotation of redundancy or surplus.

In historical medicine, plethora described an overabundance of blood in the circulation, a concept rooted in humoral theory. Physicians noted facial fullness, headaches, or a sense of congestion as signs of plethora. With advances in physiology, the term was reframed and fell from clinical use as a diagnosis; today conditions of excess blood count are labeled polycythemia.

Other uses include venous plethora in anatomy describing engorgement of veins; in physiology and medical imaging, plethysmography measures changes in volume within an organ or body part, such as limb volume with air or optoelectronic methods. The adjective plethoric describes something characterized by fullness or excessive abundance; in everyday language, plethora is often used figuratively to describe an overabundance of options, data, or information.

Related terms include plenitude, abundance, and surfeit. In medical contexts, plethysmography refers to techniques that quantify volume changes, while polycythemia denotes an actual medical condition involving increased red blood cell mass.