epifluorescencePronunciation: /ˌɛpɪflʊəˈrɛs(ə)ns, -flɔː-/Definition of epifluorescence noun [mass noun] Optics the fluorescence of an object in an optical microscope when irradiated from the viewing side. epifluorescence in other Oxford dictionaries Definition of epifluorescence in the US English dictionary