No other dictionary records the history of English words and their meanings in such depth. It not only has current words but words that have died out since 1150. It has, for example, all the words Shakespeare used and how he meant them.
The full OED exists online, but you have to pay so much a month to see it. There is a much shorter Oxford dictionary online that is free.
Samuel Johnson wrote the first English-to-English dictionary in 1755. By the middle 1800s it had begun to show its age, even with the changes they made to keep it current. A new dictionary was needed. The answer was the OED.
How to make the OED:
- Create the corpus: gather as many examples of English written since 1150 as can be found. Include all the works of recognized authors such as Shakespeare, Milton and so on.
- Read the corpus: Have readers read the corpus looking for new words, new meanings of old words and older examples of known meanings of words. The reader writes the word and the passage on a slip of paper along with where the passage came from and when it was written.
- Write the definitions: Gather all the slips for a given word and put them in order from oldest to newest. Read through them and write the definitions that will cover the examples. Support each definition with a passage that uses it.
This is slow: it took 49 years — from 1879 to 1928 — to go from A to Z.
But because English is ever-changing, even today they are still looking for new words and meanings and adding to the dictionary. The corpus is now a billion words long, coming chiefly from the Internet (including blog postings!). That is a thousand times longer than the Brown Corpus used to make the first American Heritage dictionary in the 1960s.
The first and second steps can now be largely done by computers. Step three is still a human affair.
From 1999 to 2010 the entire OED is being redone. Every definition is being made current. Some of them have not changed in over a century.
In theory the OED could make a dictionary for any dialect of English for any period in history since 1150. In practice it makes dictionaries of current English and for certain dialects, like those of America and South Africa.
Spelling: in general the OED follows British spelling with the chief exception of:
- It uses -ize instead of -ise: recognize, not recognise.
Note that the OED uses the British -yse not the American -yze: analyse, not analyze.