from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. Chemical decomposition induced by light or other radiant energy.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Any chemical reaction in which a compound is decomposed after absorbing a photon

from The Century Dictionary and Cyclopedia

  • n. In botany, the movements of protoplasm under the influence of light: distinguished as apostrophe and epistrophe.


From Ancient Greek φωτ- (phōt-), root of φῶς (phōs, "light") + λύσις (lusis, "decomposition"). (Wiktionary)



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