fluo·res·ce·in, fluo·res·ce·ine, flu·o·res·ce·ïn n. Chem. A yellowish red, crystalline substance, C20H12O5, produced by heating together phthalic anhydride and resorcin; -- so called, from the very brilliant yellowish green fluorescence of its alkaline solutions. It has acid properties, and its salts of the alkalies are known to the trade under the name of uranin.
 Syn: -- fluorescein, fluorescent dye, resorcinolphthalein.
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 fluoresceine
      n : a yellow dye that is visible even when highly diluted; used
          as an absorption indicator when silver nitrate solution
          is added to sodium chloride in order to precipitate
          silver chloride (turns pink when no chloride ions are
          left in solution and negative fluorescein ions are then
          absorbed) [syn: fluorescein, fluorescent dye, resorcinolphthalein]