PLETHYSMOGRAPH

noun Etymology: International Scientific Vocabulary, from Greek plēthysmos increase, from plēthynein to increase, from plēthys mass, quantity, from plēthein Date: 1872 an instrument for determining and registering variations in the size of an organ, limb, or part resulting from changes in the amount of blood present or passing through it, ~ic adjective ~ically adverb ~y noun