phot-
combining form
variants or photo-
1
: light : radiant energy
photon
photography
2
: photograph : photographic
photoengraving
3
: photoelectric
photocell
Word History
Etymology
Greek phōt-, phōto-, from phōt-, phōs — more at fancy
Medical Definition
phot
noun
ˈfōt 
: the cgs unit of illumination equal to one lumen per square centimeter