1. n.1 the sixteenth letter of the Greek alphabet.
2 (as π.) the symbol of the ratio of the circumference of a circle to its diameter (approx. 3.14159).
Phrases and idioms:
pi-meson PION.
Etymology: Gk: sense 2 f. Gk periphereia circumference 2. adj. Brit. sl. pious.
Phrases and idioms:
pi jaw a long moralizing lecture or reprimand.
Etymology: abbr. 3.
US var. of PIE(3).