(fō′ton) noun Physics
A quantum of light or other electromagnetic radiation. [<PHOTO- + (ELECTR)ON]
—pho·ton′ic adjective

(fō′ton) noun
A keyboard-operated machine assembly for the composition of printed matter by means of high-speed photography and photoelectric action geared to a matrix disk bearing the required characters in a series of concentric fonts, thus eliminating the use of metal type: a trade name.