Wiktionary
fluorone
n. (context chemistry English) A tricyclic heterocyclic ketone that is the basis of a class of synthetic dyestuffs.
Wikipedia
Fluorone
Not to be confused with fluorene, fluorenone, or fluorine.
Fluorone is a heterocyclic chemical compound. It forms the core structure for various chemicals, most notably fluorone dyes, including fluorescein, erythrosine and rhodamine. It is an isomer of xanthone, sometimes referred to as an isoxanthone.