
Number
A number is a mathematical object used to count, measure and also label. The original examples are the natural numbers 1, 2, 3, 4 and so forth. A notational symbol that represents a number is called a numeral. In addition to their use in counting and measuring, numerals are often used for labels (as with telephone numbers), for ordering (as with serial numbers), and for codes (as with ISBNs). In common usage, number may refer to a symbol, a word, or a mathematical abstraction.
In mathematics, the notion of number has been extended over the centuries to include 0, negative numbers, rational numbers such as 1/2 and −2/3, real numbers such as √2 and π, and complex numbers, which extend the real numbers by adding a square root of −1. Calculations with numbers are done with arithmetical operations, the most familiar being addition, subtraction, multiplication, division, and exponentiation. Their study or usage is called arithmetic. The same term may also refer to number theory, the study of the properties of numbers.
Besides their practical uses, numbers have cultural significance throughout the world. For example, in Western society, the number 13 is regarded as unlucky, and “a million” may signify “a lot.” Though it is now regarded as pseudoscience, numerology, the belief in a mystical significance of numbers, permeated ancient and medieval thought. Numerology heavily influenced the development of Greek mathematics, stimulating the investigation of many problems in number theory which are still of interest today.During the 19th century, mathematicians began to develop many different abstractions which share certain properties of numbers and may be seen as extending the concept. Among the first were the hypercomplex numbers, which consist of various extensions or modifications of the complex number system. Today, number systems are considered important special examples of much more general categories such as rings and fields, and the application of the term “number” is a matter of convention, without fundamental significance.

Numeral (noun)
A symbol that is not a word and represents a number, such as the Arabic numerals 1, 2, 3 and the Roman numerals I, V, X, L.

Numeral (noun)
A word representing a number.

Numeral (noun)
A card whose rank is a number (usually including the ace as 1).
“Jacks, queens, and kings are not numerals.”

Numeral (adjective)
Of or relating to numbers; numerical.

Number (noun)
An abstract entity used to describe quantity.
“Zero, one, 1, 2.5, and pi are all numbers.”

Number (noun)
A numeral: a symbol for a nonnegative integer.
“The number 8 is usually made with a single stroke.”

Number (noun)
A member of one of several classes: natural numbers, integers, rational numbers, real numbers, complex numbers, quaternions.
“The equation e^{ipi}+1=0 includes the most important numbers: 1, 0, pi, i, and e.”

Number (noun)
Indicating the position of something in a list or sequence. Abbreviations: No or No., no or no. (in each case, sometimes written with a superscript “o”, like Nº or №). The symbol “#” is also used in this manner.
“Horse number 5 won the race.”

Number (noun)
Quantity.
“Any number of people can be reading from a given repository at a time.”

Number (noun)
A sequence of digits and letters used to register people, automobiles, and various other items.
“Her passport number is C01X864TN.”

Number (noun)
A telephone number.

Number (noun)
Of a word or phrase, the state of being singular, dual or plural, shown by inflection.
“Adjectives and nouns should agree in gender, number, and case.”

Number (noun)
Poetic metres; verses, rhymes.

Number (noun)
A performance; especially, a single song or song and dance routine within a larger show.
“For his second number, he sang “The Moon Shines Bright”.”

Number (noun)
A person.

Number (noun)
An item of clothing, particularly a stylish one.

Number (noun)
A marijuana cigarette, or joint; also, a quantity of marijuana bought form a dealer.

Number (noun)
An issue of a periodical publication.
“the latest number of a magazine”

Number (verb)
To label (items) with numbers; to assign numbers to (items).
“Number the baskets so that we can find them easily.”

Number (verb)
To total or count; to amount to.
“I don’t know how many books are in the library, but they must number in the thousands.”