What does eosine mean?
Eosine is a variant spelling of eosin, a synthetic red dye belonging to the fluorescein family. Produced by treating fluorescein with bromine, it is a strongly coloured compound that also fluoresces, glowing greenish under ultraviolet light. Its chief use today is in biology and medicine: combined with haematoxylin, it forms the classic H&E stain that pathologists rely on to reveal the structure of cells and tissues, colouring cytoplasm and collagen pink against blue-purple nuclei. In its late-nineteenth-century heyday, however, eosine was better known outside the laboratory, serving as a brilliant reddish pigment in cosmetics, inks, and dyes. The name derives from Greek ēōs, meaning dawn, a reference to its rosy hue. Although the spelling 'eosine' has largely given way to 'eosin' in contemporary scientific usage, both forms denote the same substance, which remains one of the most widely used stains in medical diagnostics.
nounA red fluorescent dye, a brominated derivative of fluorescein, used chiefly as a biological stain and formerly in cosmetics and inks. Eosine is a less common spelling of eosin.
- The red fluorescent dye eosin (a brominated fluorescein derivative) used as a biological stain, especially in haematoxylin–eosin staining of tissue sections.
- Formerly, a reddish cosmetic or ink colourant based on this dye.
"The histology lab stained the tissue sections with eosine to highlight the cell structures under the microscope."
"The pathologist examined slides stained with haematoxylin and eosine to identify abnormalities in the biopsy."
"In the nineteenth century, eosine was prized as a vivid pink-red colouring for lipsticks and writing inks."
Rarely pluralised; when it occurs, the plural typically refers to different commercial grades or formulations of the dye.
"Early catalogues listed several eosines of varying shades for use in textile printing."
Named for the Greek goddess of dawn, this rose-red stain has been colouring microscope slides since the 1870s — and it still glows under ultraviolet light.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of eosine
Eosine was coined in the 1870s from Greek ēōs, meaning 'dawn', chosen for the dye's rosy, sunrise-pink colour; the ending '-ine' is the standard chemical suffix for dyes and alkaloids. It was first marketed by German chemical firms shortly after fluorescein's discovery, and the shorter form 'eosin' soon became the preferred English spelling. Related coinages sharing the same Greek root include eosinophil, the name of a type of white blood cell that readily takes up the acidic dye.
Related word forms
How eosine is actually used
The spelling 'eosine' is now uncommon; modern scientific literature almost always uses 'eosin'. The word belongs to formal technical register, encountered mainly in histology, pathology, and histories of chemistry.
Easily confused with eosine
Eosin is the standard modern spelling of the same dye; 'eosine' is an older or variant spelling referring to the identical substance.