As of today, i'm starting to use the 1913 Websters and WordNet, using the OmniDictionary application on the Mac.
My version of beloved American Heritage Dictionary on my Mac, bought in 1995 for Mac OS, has been running under Classic environment in Mac OS X since about 2002. As of today in 2007, Classic is getting obsolete. New Macs haven't included it since the Intel Macs in 2006. So, am looking for a replacement. (See: Review: American Heritage Dictionary vs Merriam Webster Collegiate)
The American Heritage Dictionary is freely available on several websites. The minor problem with using websites is that it's not as quick or convenient as the hard disk version. Two more important misgivings with website versions is that (as far as i know) they don't have a “Word Hunter™” feature, which allows you to search words thru their definitions (e.g. find all words whose def contains “pedantic”), and they don't have a wild card feature, which allows you to find words with unspecified run of letters (e.g. find all words ending in “ology”). (these capabilities are probably in some website somewhere.)
OmniDictionary is a Mac application that gets definition from several online resources. A few of primary interest is 1913 Websters, WordNet, CIA World Fact book 2002.
The value of The World Factbook needs not to be spoken here. Here we'll look at 1913 Websters and WordNet. As a English reference, it is important for me to know its credential and qualifications, in particular its history.
So, what's this Webster? Wikipedia comes to the rescue: Webster's Dictionary. In short, 1913 Websters is a authoritative dictionary at the time. This is good for me because as a hobbyist doing occasional linguistic research, old dictionary is a excellent resource to get a word's nuances and history.
What's WordNet? Wikipedia WordNet article indicates that it's a collection of lexicon organized in a (linguistic) semantic net for the purposes of aiding machine translation or other general artificial intelligence applications.
This is fantastic, because this is a different approach than all the traditional dictionaries in their variations and arguments of description or prescription or etymology. WordNet, its nature and methodology, is based on linguistic, statistical means, as opposed to the human elements and expert's biases.
Since early 2008, i've stopped using OmniDictionary app, instead, i use emacs for looking up dictionary at “dict.org”. For detailed how-to, see: Emacs: Perl PHP Dictionary Wikipedia Google … Reference lookup.