1. (noun)phosphorus, P, atomic number 15 a multivalent nonmetallic element of the nitrogen family that occurs commonly in inorganic phosphate rocks and as organic phosphates in all living cells; is highly reactive and occurs in several allotropic forms Synonyms: daystar, atomic number 15, phosphorus, morningstar
2. (noun)P, p the 16th letter of the Roman alphabet Synonyms: atomic number 15, phosphorus