Meaning

noun the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846...

noun someone who can be employed as a detective to collect information

noun the scientist in charge of an experiment or research project

originFrom Koine Greek πῖ (pî), from Ancient Greek πεῖ (peî), ultimately from Proto-Semitic *pay- (“mouth”). Doublet of pe. Its mathematical use apparently stems from its use as the first letter in περιφέρεια (periphéreia, “periphery; circumference”) and was first cited in 1706 in the Synopsis Palmariorum Matheseos by William Jones.

Etymology from Wiktionary, CC BY-SA 3.0