Is it ensure, insure, or assure?
Greek letter, from Hebrew, literally "little mouth." As the name of the mathematical constant, from 1841 in English, used in Latin 1748 by Swiss mathematician Leonhart Euler (1707-1783), as an abbreviation of Greek periphereia "periphery." For the meaning "printer's term for mixed type," see pie (3).
The Greek letter pi. Entries beginning with this character are alphabetized under pi.
n. pl. pis
Symbol π The 16th letter of the Greek alphabet.
The pH value for the isoelectric point of a given substance in solution.