Source : Webster's Revised Unabridged Dictionary (1913)

Eosin \E"o*sin\, n. [Gr. ? dawn.] (Chem.)
   A yellow or brownish red dyestuff obtained by the action of
   bromine on fluoresce["i]n, and named from the fine rose-red
   which it imparts to silk. It is also used for making a fine
   red ink. Its solution is fluorescent.

Source : WordNet®

eosin
     n : a red fluorescent dye resulting from the action of bromine
         on fluorescein; used in cosmetics and as a biological
         stain for studying cell structures [syn: {bromeosin}]