• (n.) A yellow crystalline dyestuff, regarded as a glucoside, extracted from a species (Rhamnus Frangula) of the buckthorn; -- called also rhamnoxanthin.
Fran'gu·lin noun (Chemistry) A yellow crystalline dyestuff, regarded as a glucoside, extracted from a species ( Rhamnus Frangula ) of the buckthorn; -- called also rhamnoxanthin . 
Type: Term Pronunciation: frang′gū-lin Definitions: 1. A glycoside from frangula; has been used as a purgative. Synonyms: rhamnoxanthin
Frangulin is a yellow crystallisable dye extracted from the bark of the alder. It is used to dye wool, silk and cotton.