photo-

  1. a combining form meaning “light” (photobiology); also used to represent “photographic” or “photograph” in the formation of compound words: photocopy.
Also especially before a vowel, phot-.

Origin of photo-

< Greek, combining form of phôs (genitive phōtós)
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for photo-

photo-

combining form
  1. of, relating to, or produced by lightphotosynthesis
  2. indicating a photographic processphotolithography

Word Origin for photo-

from Greek phōs, phōt- light
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for photo-

word-forming element meaning "light" or "photographic" or "photoelectric," from Greek photo-, comb. form of phos (genitive photos) "light," from PIE root *bha- "to shine" (see phantasm).

Online Etymology Dictionary, © 2010 Douglas Harper

photo- in Medicine

photo-

pref.
  1. Light; radiant energy:photosynthesis.
  2. Photographic:photofluorography.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

photo- in Science

photo-

  1. A prefix that means “light,” as in photoreceptor.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.