The only paper dictionary worth having.

''Except for the 'New Oxford Dictionary of English'.''

Look for the 3-volume 1933 edition (+1975 supplement) available from most good used book stores for a song.

OED is also available online: http://www.oed.com/.  It's the only dictionary you'll ever need.  Unfortunately, it requires registration ($$), but many colleges and universities have a site-subscription for it.
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Among the most renowned dictionaries of the English language. It is the largest and the most complete English dictionary ever compiled (20+ volumes)

It is based on historic principles. For many words, you have examples of usage dating back to many centuries. 

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See also MerriamWebsterDictionary for a free on-line resource!

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