The Oxford English Dictionary (OED), published by the Oxford University Press, is a descriptive (as opposed to prescriptive) dictionary[1] of the English language. As well as describing English usage in its many variations throughout the world, it traces the historical development of the language, providing a comprehensive resource to scholars and academic researchers.The second edition, published in 1989, came to 21,728 pages in 20 volumes.
No, I haven't read every word (!), but I've lived with the OED for quite a few years, first in the compact edition, and more recently also in the 20-volume set plus the supplements, and I have read all the introductory section. Mainly it's a merger of the 12-volume first edition, originally published in parts between 1884 and 1928, with the 4-volume supplement published between 1972 and 1986; thus it's a record of the language up to a bit past the mid-20th century, and so it's my first port of call when I need to look up something found in a book from that period or earlier: the OED often gives me the information I need faster than an online search. (In similar vein, I recall a recent reviewer of Johnson's Dictionary saying he found that more useful than modern dictionaries when he's reading older authors such as William Blake.)
The pronunciations given are stated to be "those in use in the educated speech of southern England (the so-called 'Received Standard')." This is what I was taught to speak when I was educated in the 1950s and 1960s. Younger people no longer seem to learn it; almost everybody now speaks with a local accent, such as Estuary English in South-East England. I wonder how future dictionaries are going to indicate pronunciation when there is no longer a standard!
For an avid reader and lover of the language, the OED is a treasure for a lifetime.