noun

1. An abstract entity used to describe quantity.

   “Zero, one, −1, 2.5, and pi are all numbers.”

2. A numeral: a symbol for a non-negative integer.

   “The number 8 is usually made with a single stroke.”

3. An element of one of several sets: natural numbers, integers, rational numbers, real numbers, complex numbers, and sometimes extensions such as hypercomplex numbers, etc.

   “The equation e^{i\pi}+1=0 includes the most important numbers: 1, 0, \pi, i, and e.”

Synonyms: numeral, rime, scalar

verb

1. To label (items) with numbers; to assign numbers to (items).

   “Number the baskets so that we can find them easily.”

2. 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.”