/ Dictionary / Index P photochemistry: Meaning and Definition of Find definitions for: pho•to•chem•is•try Pronunciation: (fō"tō-kem'u-strē), [key] — n. the branch of chemistry that deals with the chemical action of light. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: photochemistry (Thesaurus) photochemical smog photochromic Related Content Daily Word Quiz: inutiae Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language