1The sixteenth letter of the Greek alphabet (Π, π), transliterated as ‘p’.
- 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']
- 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.
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