1909, a type of copying machine (trademark Commercial Camera Company, Providence, R.I.) whose name became a generic noun and verb (1914) for "photocopy;" from photo- + -stat.
Entries linking to photostat
photo-
word-forming element meaning "light" or "photographic" or "photoelectric," from Greek photo-, combining form of phōs (genitive phōtos) "light" (from PIE root *bha- (1) "to shine").
-stat
word-forming element used in making names of devices for stabilizing or regulating (such as thermostat), from Greek statos "standing, stationary," from PIE *ste-to-, suffixed form of root *sta- "to stand, make or be firm." First used in heliostat "an instrument for causing the sun to appear stationary" (1742). Related: -static.