1794, "mechanical device for making multiple copies of something written or drawn," from Greek polygraphos "writing much," from polys "much" (see poly-) + graphos "writing," from graphein "to write" (see -graphy).
Meaning "instrument for recording several pulsations of the body at the same time" is 1871; first used as a lie detector 1921. Related: Polygraphy (1590s); polygraphic (1771).
polygraph pol·y·graph (pŏl'ē-grāf')
An instrument that simultaneously records changes in physiological processes such as heartbeat, blood pressure, and respiration.