Толковый словарь английского языка Oxford English Reference - pi

1. n. 1 the sixteenth letter of the Greek alphabet. 2 (as &pi.) 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).