fluorine: a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite
abstraction: a general concept formed by extracting common features from specific examples
ground cherry: any of numerous cosmopolitan annual or perennial herbs of the genus Physalis bearing edible fleshy berries enclosed in a bladderlike husk; some cultivated for their flowers