an instrument for the simultaneous electrical or mechanical recording of several involuntary physiological activities, including blood pressure, skin resistivity, pulse rate, respiration, and sweating, used esp as a would-be lie detector
a device for producing copies of written, printed, or drawn matter
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).