eosin

UK: /ˈiːəʊsɪn/ US: (ē′ə sin)

WordReference Random House Unabridged Dictionary of American English © 2026

e•o•sin  (ē′ə sin), n. [Chem.]

1. Chemistry Also called bromeosin, tetrabromofluorescein. a red, crystalline, water-insoluble solid, C₂₀H₈Br₄O₅, derived from fluorescein by bromination: used chiefly as an acid dye for dyeing silk a rose red color and as a histological stain.
2. Chemistry any of a variety of eosinlike dyes.

Also, e•o•sine  (ē′ə sin, -sēn′). 

• Greek ēó̄s dawn (see eo-) + -in²
• 1865–70

e′o•sin′ic, adj. 
e′o•sin•like′, adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

eosin / ˈiːəʊsɪn/, eosine / ˈiːəʊsɪn -ˌsiːn/ noun

1. Also called: bromeosin a red crystalline water-insoluble derivative of fluorescein. Its soluble salts are used as dyes. Formula: C₂₀H₈Br₄O₅
2. any of several similar dyes

Etymology: 19th Century: from Greek ēōs dawn + -in; referring to the colour it gives to silk