For several decades now, THE MERRIAM-WEBSTER'S COLLEGIATE DICTIONARY has served as the standard American English dictionary. I have done a good deal of copyediting over the years, and every publisher I have worked with has specified this dictionary (along with the Webster's Unabridged) as the standard governoring the way that American English words are spells and defined. Although one can feel overwhelmed by the sheer number of dictionaries in the reference section of any good bookstore, this volume is as close to authoritative as we have in the United States. One might have a preference for another, but this is the only one that enjoys widespread authoritative acceptance.
The dust jacket explains the ways that the new 11th edition has been expanded, but personally, while I am quite certain that it has been expanded, I have not noticed a great deal of difference from the 10th edition. It may be definitive and improved, but most of the improvements will be difficult for anyone to detect. The new CD-ROM included with it, however, is a vast improvement on the previous software that was developed based on the 10th edition. When the 10th edition first came out, CD software was not widely available. A CD version of the dictionary did eventually come out, but it was somewhat rudimentary. The new CD-ROM, however, is a huge improvement. For instance, when looking up any word, a column will display a number of words that approximate the word that your are attempting to look up. If you can merely approximate the spelling, you can frequently find the correct word. Furthermore, by double clicking on any word in the online dictionary, you will pull up the listing for that word. The CD-ROM also has a link to the Internet.
Let's face it. Buying dictionaries for most people is about as exciting as having one's oil changed. But like oil changes, dictionaries are essential. For the foreseeable future, this one is going to remain the definitive American English dictionary.