Any of several vivid red, oil-soluble azo dyes, especially (in full "Oil Red O") one having the formula C₂₆H₂₄N₄O, used as a histological stain for lipids.
Origin
1920s.
Definition of Oil Red in US English:
Oil Red
noun
Chemistry
Any of several vivid red, oil-soluble azo dyes, especially (in full "Oil Red O") one having the formula C₂₆H₂₄N₄O, used as a histological stain for lipids.