photon

Etymology

From photo- + -on. Coined by American physicist Leonard Troland in 1916 as a unit of light hitting the retina, and later popularized in a more modern sense by Gilbert N. Lewis, with the term gaining acceptance in the physics community by the late 1920s.

noun

1. (physics) The quantum of light and other electromagnetic energy, regarded as a discrete particle having zero rest mass, no electric charge, and an indefinitely long lifetime. It is a gauge boson.
   The single-imaging optic of the mammalian eye offers some distinct visual advantages. Such lenses can take in photons from a wide range of angles, increasing light sensitivity. They also have high spatial resolution, resolving incoming images in minute detail. 2013 July-August, Fenella Saunders, “Tiny Lenses See the Big Picture”, in American Scientist