There are 3 main definitions of PI in English:

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PI 1

Entry from US English dictionary

abbreviation

Private investigator.

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Syllabification: PI

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There are 3 main definitions of PI in English:

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pi 2

Pronunciation: /pʌɪ/

noun

1The sixteenth letter of the Greek alphabet (Π, π), transliterated as ‘p’.
Example sentences
  • This is true of no other letter of the alphabet except pi, and here the name is a natural development of the Semitic name pe.
  • Pi is the sixteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 80.
  • The western Greek alphabet changed pi into a backwards loop shape.
1.1The numerical value of the ratio of the circumference of a circle to its diameter (approximately 3.14159).
From the initial letter of Greek periphereia 'circumference'
Example sentences
  • Saying that pi is 3.14 without addressing the fact that it goes on infinitely afterward overlooks the true essence of the number.
  • So far, pi has been calculated to 1.24 trillion decimal places with the aid of a supercomputer.
  • The circumference of a circle can be found by multiplying pi (which is equal to 3.14) by the diameter of the circle.
1.2 (Pi) [followed by Latin genitive] Astronomy The sixteenth star in a constellation: Pi Herculis
More example sentences
  • Lower letters are generally assigned to brighter stars, but a star designated pi is not necessarily the 16th brightest star of the constellation (for example, pi Puppis is number two in brightness in the constellation Puppis).
  • Pi Herculis is particularly noticeable for its reddish complexion and is an excellent place to begin studying the constellation.
  • The red giant Pi Leonis in the constellation of Leo the Lion has a radius 80 times larger than our own Sun.
1.3 [as modifier] Chemistry & Physics Relating to or denoting an electron or orbital with one unit of angular momentum about an internuclear axis: the π orbital system of the benzene molecule
More example sentences
  • Both of the electrons in the pi bond are found in the pi bonding orbital.
  • The lowest pi orbital of benzene is called the A2u orbital.
  • The bonding pi orbital is lower in energy than the atomic p orbitals, whereas the antibonding pi orbital is higher in energy than the atomic pi orbitals.

symbol

1 (π) The numerical value of pi.

Origin

Greek.

Words that rhyme with pi

ally, Altai, apply, assai, awry, ay, aye, Baha'i, belie, bi, Bligh, buy, by, bye, bye-bye, chi, Chiangmai, Ciskei, comply, cry, Cy, Dai, defy, deny, Di, die, do-or-die, dry, Dubai, dye, espy, eye, fie, fly, forbye, fry, Frye, goodbye (US goodby), guy, hereby, hi, hie, high, I, imply, I-spy, July, kai, lie, lye, Mackay, misapply, my, nearby, nigh, Nye, outfly, passer-by, phi, pie, ply, pry, psi, Qinghai, rai, rely, rocaille, rye, scry, serai, shanghai, shy, sigh, sky, Skye, sky-high, sly, spin-dry, spry, spy, sty, Sukhotai, supply, Tai, Thai, thereby, thigh, thy, tie, Transkei, try, tumble-dry, underlie, Versailles, Vi, vie, whereby, why, wry, Wye, xi, Xingtai, Yantai

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There are 3 main definitions of PI in English:

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pi 3

Pronunciation: /pʌɪ/

adjective

British informal
Short for pious.

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