a lighting fixture that uses a fluorescent lamp
"The classroom was brightly lit by rows of old fluorescent lights that hummed softly overhead."
A fluorescent light.
"The harsh glow from the fluorescent light made her squint as she worked late into the night."
emitting light during exposure to radiation from an external source
"The fluorescent paint on the safety vest glows brightly under ultraviolet light."
Of or relating to fluorescence.
"The fluorescent material glowed brightly under ultraviolet light, emitting a visible spectrum that was distinct from its absorption peak."
In plain English: Fluorescent means glowing with bright light when hit by other energy, often making things look more vivid than they really are.
"The fluorescent lights in the office hummed loudly all day long."
The word comes from Latin fluere, meaning "to flow," combined with a suffix to describe something that flows or glows. It entered English in the late 19th century to name substances that emit visible light when exposed to ultraviolet radiation, shifting from its original sense of simply flowing.