Pi Day Vocabulary

Learn these words relating to pi, the mathematical constant and the 16th letter of the Greek alphabet. Pi Day is celebrated on March 14th, or 3/14, the date that corresponds to the first (and most well-known) digits in the decimal form of Pi.

Activities for this list:

definitions & notes only words
  1. approximation
    a rough calculation of quantity or degree or worth
    The earliest written approximations of pi are 3.125 in Babylon (1900-1600 B.C.) and 3.1605 in ancient Egypt (1650 B.C.). - Scientific American (Mar 14, 2016)
  2. calculate
    make a mathematical computation
    Pi has been calculated to over one trillion digits.
    To calculate is to do some arithmetic, like if you calculated that you were three miles from home or owed twenty dollars for dinner plus tip. Besides math, this word is used metaphorically for others kinds of figuring out. Often, calculating is a synonym for thinking. In that figurative sense, calculate has a bit of a heartless connotation. A ruthless, severe person can be described as cold and calculating.
  3. circumference
    the length of the closed curve of a circle
    The circumference of a circle is the linear distance around it, and is a special case of perimeter.
  4. constant
    a number representing a quantity with a fixed value
    Pi is a constant number, meaning that for a circle of any size the ratio of the circumference to the diameter will be the same.
  5. decimal
    a proper fraction whose denominator is a power of 10
    Pi can be calculated out to an infinite number of digits beyond the decimal point, but the first five digits are 3.1415.
  6. diameter
    the length of a straight line through the center of a circle
    ...39 digits are sufficient to perform most cosmological calculations, because that’s the accuracy necessary to calculate the circumference of the observable universe to within one atom’s diameter. - Scientific American (Mar 14, 2016)
  7. digit
    one of the elements that form a system of numeration
    People have enjoyed memorizing the digits in pi since at least the beginning of the 19th century. Back then only a few hundred digits were known.
  8. formula
    a group of symbols that make a mathematical statement
    The formula for calculating the area of a circle uses π, the mathematical constant.
  9. fraction
    a small part or item forming a piece of a whole
    π is an irrational number, and cannot be expressed as a common fraction.
    A fraction is a part of something. In math, that means a number such as ¼ or 12/8. When people use the word more loosely, it usually refers to a tiny part of something: just an itty-bitty bit. If a fraction of voters support blowing up the moon, that doesn’t indicate a ton of support, which is understandable, because what did the moon do to anybody?
  10. geometry
    the mathematics of points and lines and curves and surfaces
    The number pi is used when solving geometry problems involving circles, spheres and ellipses.
  11. infinite
    having no limits or boundaries in time or space
    The first written description of an infinite series that could be used to compute pi was laid out in Sanskrit verse by Indian astronomer Nilakantha Somayaji around 1500 A.D. - Scientific American (Mar 14, 2016)
    An infinite number—like Pi—has no end. You could never get to the end of it, even if you kept counting all day, every day, for the rest of your life. An infinite number, like numbers themselves, never ends, man. The noun form is infinity, which can apply to anything without an end or limit. The upcoming superhero blockbuster Avengers: Infinity War is named for the Infinity Gauntlet, a glove-like weapon that gives the wearer limitless power and is on my Christmas list.
  12. irrational
    a number that cannot be expressed as a quotient of integers
    ...pi is an irrational number, meaning that its decimal form neither ends (like 1/4 = 0.25) nor becomes repetitive (like 1/6 = 0.166666...). - Scientific American
  13. mathematician
    a person skilled in the logic of quantity and arrangement
    The symbol π was adopted in 1706 by British mathematician William Jones and was made popular by Swiss mathematician Leonhard Euler in 1737.
  14. pi
    the ratio of the circumference to the diameter of a circle
    Pi (π) is the ratio of a circle’s circumference to its diameter.
  15. radius
    a straight line from the center to the perimeter of a circle
    Pi also appears in the calculations to determine the area of an ellipse and in finding the radius, surface area and volume of a sphere. - Scientific American (Mar 14, 2016)
  16. ratio
    the relative magnitudes of two quantities
    The ratio has been calculated to over one trillion digits beyond the decimal point.
  17. value
    a numerical quantity measured or assigned or computed
    Our world contains many round and near-round objects; finding the exact value of pi helps us build, manufacture and work with them more accurately. - Scientific American (Mar 14, 2016)
  18. transcendental
    existing outside of or not in accordance with nature
    Pi also opens a window into a more uncharted universe, the one consisting of transcendental numbers, which exclude such common irrationals as square and cube roots. - New York Times (Mar 13, 2015)
  19. random
    lacking any definite plan or order or purpose
    So what use have all those digits been put to? Statistical tests have suggested that not only are they random, but that any string of them occurs just as often as any other of the same length. - New York Times (Mar 13, 2015)
  20. integer
    any natural number or its negative, or zero
    At some point in your life, you were most likely taught how to round integers and decimal numbers to some specified number of digits or decimal places.Scientific American (Dec 18, 2013)
    Fractions are parts of numbers, but plenty of numbers are whole and complete, thank you very much. A fancy math term for a whole number is integer. 34 is an integer, but ¾ is not. Whole doesn’t have to mean positive: -34, -9000, and -2 are all integers too.

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