The Collaborative International Dictionary of English v.0.48:
fluorescein \fluo`res"ce*in\, fluoresceine \fluo`res"ce*ine\,
fluorescein \flu`o*res"ce*["i]n\, 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.
[1913 Webster]