Pis

Part of speech: noun

Definitions

1. The plural form of pi, whether referring to the Greek letter or the mathematical constant approximately equal to 3.14159
2. Multiple instances of the Greek letter π or the irrational number used to calculate the circumference and area of circles
3. The plural of pi, denoting either several Greek letters or multiple uses of the mathematical ratio of a circle's circumference to its diameter

Etymology: The plural "pis" is simply the plural of "pi", so the story belongs to the Greek letter. Pi comes from the Greek letter π, and the mathematical symbol likely arose because the letter opens the Greek word "periphéreia", meaning periphery or circumference. The ratio of a circle's circumference to its diameter was written with this letter, and the first recorded use in this sense appears in 1706, in the "Synopsis Palmariorum Matheseos" by William Jones. Where the letter came from is less certain. It is probably a Greek borrowing from a Phoenician letter, and the name's origin is murky. Writers also sometimes use "pi" in other senses, such as a common example of a non-alphabetic character, or a printers' term for jumbled type, though the link to "pica" or "pied" is uncertain.