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When learning about numbers, it's easy just to think about the number symbols. But numbers can be described as words as well. We learn these words as children, or even babies, long before we meet our 1,2,3. Enter a number to see what the words are, or click on Count numbers. It will work up to the trillions.
We use these words when we talk of numbers, unless we are describing a long number, like a telephone number. Even then, we use the words for the digits. However, if we write numbers, we usually use the symbols instead. There is one exception. Cheques are written using words as well as numbers. Numbers can be altered quite easily. Words are harder!
If this was a number system, then it wouldn't be unary or positional. You might think it was positional, as the same numbers get used no matter how large the number is. You say two thousand and two. But you need the word thousand to tell you how big the first two is. There is a word for zero, but you don't use it inside a number. For example, you don't say two thousand, zero hundreds, zero tens and two.
A prefix is part of a word, at the front. There are prefixes which describe numbers. For example, a hemisphere is half a sphere. There is more than one prefix for each number as they come from different languages (usually Latin or Greek), or they are spelled different ways in different words.
Semi, hemi, demi  1/2 
Uni  1 
Bi, di  2 
Tri, ter  3 
Tetra, tetr, tessera, quadri, quadr  4 
Pent, penta, quinqu, quinque, quint  5 
Sex, sexi, hex, hexa  6 
Hept, hepta, sept, septi, septam  7 
Oct, octa, octo  8 
Non, nona, ennea  9 
Dec, deca  10 
Hendca, undec, undeca  11 
Dodeca  12 
Trideca  13 
Quindeca  15 
Icos, icosa, icosi  20 
Incidentally, the irrational fear of the number 13 is Triskaidekaphobia which comes from the Greek tris (three) + kai (and) + deka (ten).
Some numbers have special words.
2  a couple  In metric measurement, the most important number is ten. But in Imperial Measures, many other numbers were important. Every British school child used to know that there were twelve inches in a foot. Before 1971, even the British money was different, and there were twelve old pennies in a shilling, and twenty shillings in a pound. So you can see that twelve (or a dozen) and twenty (or a score) were important numbers. 
2  a pair  
2  a brace  
6  half a dozen  
12  a dozen  
13  a baker's dozen  The baker's dozen was socalled because a baker used to give an extra roll if you asked for a dozen. The reason was to prevent being prosecuted for short weight. Bread was the staple diet in England in mediaeval times and had to be a certain weight. It is difficult to bake bread to a particular weight, so when a person ordered a dozen the thirteenth loaf was added to make sure it was not underweight. 
20  a score  
144  a gross (12 dozen)  
1728  a great gross (12 gross) 


British English and American English used to have different meanings for 'billion' and 'trillion'. The British used to use a billion to mean a million million and a trillion to mean a million million million but now they use these words in the same way as the Americans. A billion is a thousand million or 1,000,000,000. A trillion is a million million, or 1,000,000,000,000.
Children often invent words for 'really big numbers'. These don't have a standardised size, they are just indicating an enormous number. When I was young, we used zillion. Now, British children seem to use squillion or gazillion instead.
The metric system has a regular system of prefixes to describe the units. For example, a hundreth of a metre is a cetimetre, and a thousand metres is a kilometre.
Multiples

Fractions

These numbers are in a particular order. What is it?
8, 5, 4, 9, 1, 7, 6, 3, 2
The clue is in the heading. If you write the words for these numbers, they're in alphabetical order: eight, five, four, nine, one, seven, six, three, two.
Now imagine that the words for every single number is listed in alphabetical order. This is rather hard, as there are an infinite number of them! But if we did, what would the first word be? Eight. And the last would be zero!
Four is the only number in English that has the same number of letters in its name as the number itself (also in Dutch, German & Hebrew).
© Jo Edkins 2017  Return to Numbers index