Word
PI
Phoneticspi
US/ˈpaɪ/
UK/pˈaɪ/
Uncountable noun
Definition
n. a mathematical number that is roughly 3.14. You use it to calculate the area or the distance around a circle.
n. a mathematical constant representing the ratio of a circle's circumference to its diameter, approximately equal to 3.14159.
Examples
“We used pi to find the area of the circle.”
“The students were asked to calculate the volume of the cylinder using pi to two decimal places.”
“Because pi is an irrational number, its decimal representation never ends and never settles into a repeating pattern, a property that has fascinated mathematicians for centuries.”
Examples
simple
“We used pi to find the area of the circle.”
contextual
“The students were asked to calculate the volume of the cylinder using pi to two decimal places.”
complex
“Because pi is an irrational number, its decimal representation never ends and never settles into a repeating pattern, a property that has fascinated mathematicians for centuries.”
Usage
Usually written as the Greek letter π in mathematical equations.
Real-World Examples
“Pi Day, the International Day of Mathematics, is celebrated on 14 March, due to the date's American shorthand 3/14 – the first three digits of π.” “The number pi, represented by the Greek letter π, is the most famous mathematical constant in history.” “The number pi, which is celebrated with its own day on 14 March, has inspired “Pilish” – a fiendishly challenging form of writing.” “The mathematical constant pi is under threat from a group of detractors who will be marking "Tau Day" on Tuesday.” Etymology
From 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.
The origin of PI as printer's slang for a jumbled mass of type is disputed. The OED records suggestions that it derives from the Greek letter π as a familiar non-alphabetic character, from pica (the type size), or from pie or pied in reference to the mixture's checkered, multicoloured appearance — though none of these claims carries definitive evidence.
From the Greek letter π, an initialism of περίμετρος (perímetros, "perimeter, circumference") or περίμετρον (perímetron), used since the 18th century to denote the ratio of a circle's circumference to its diameter.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B2 FirstIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.5.5–6.5TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 4.0–4.572–94TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.785–944
- Frequency
- Frequent
- Level
- B2 · Upper Intermediate
- Updated
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QR code
englishreference.com/q/pi