Oxford English Dictionary
1) When capitalized, refers to the morning star (Venus, appearing in the sky before sunrise); 2) A substance or organism that emits light spontaneously or after heating or other treatment; 3) A non-metallic chemical element, atomic number 15, which is widespread (chiefly in the form of phosphates) in living organisms and in minerals, and in its commonest form is a whitish waxy solid which undergoes spontaneous oxidation (with chemiluminescence) or ignition in air. Symbol P.
Merriam-Webster Dictionary (1907)
1) Of or pertaining to phosphorus; resembling or containing phosphorus; specifically, designating those compounds in which phosphorus has a lower valence as contrasted with the phosphoric compounds; 2.1) the morning star: Phosphor; 2.2) A poisonous nonmetallic element of the nitrogen group, obtained as a white, or yellowish, translucent waxy substance, having a characteristic disagreeable smell. It is very active chemically, must be preserved in water, and unites with oxygen even at ordinary temperatures, giving a faint glow—whence its name.