A Web of On-line Dictionaries at YourDictionary.com
One-stop shopping for all things dictionary! This website indexes on-line dictionaries, thesauri, including over 800 dictionaries in 160 languages. "Preference in selection has been given to free online dictionaries of high quality." Specialized dictionaries on over 50 topics such as advertising, agriculture, architecture, biology, education, geology, law and medicine have recently been added.
OneLook Reverse Dictionary
"OneLook's reverse dictionary lets you describe a concept and get back a list of words and phrases related to that concept. Your description can be a few words, a sentence, a question, or even just a single word."
"Look up 128,000+ acronyms/abbreviations & their meanings. A searchable database containing common acronyms and abbreviations about all subjects, with a focus on computers, technology, telecommunications, and the military."
Ohio State University Glossary of Horitcultural Terms
Roget's International Thesaurus of English Words and Phrases
"Peter Roget’s classic structure coupled with Mawson’s modernization becomes even more user-friendly on Bartleby.com with 85,000 hyperlinked cross-references—thus fulfilling their goal of “each word being related to its neighbors and each part to the whole.” Additionally, over 2,900 proverbs and quotations from classic and modern authors illustrate the 1,000-plus entries."
A dictionary of information technology, Internet, and computer terms
The Word Detective
"The Word Detective on the Web is the online version of The Word Detective, a newspaper column answering readers' questions about words and language. The Word Detective is written by Evan Morris and appears in finer newspapers in the U.S., Mexico and Japan."
"The words and phrases are selected because their origins are inherently interesting or some bit of folklore, sometimes true and sometimes false, is associated with the origin."
World Wide Words
This extensive site provides information on the origins of numerous words and phrases.
The Wordsmyth English Dictionary-Thesaurus
If you're not sure about spelling, use the Approximate Search and the computer will look for near matches ("suphose" retrieved "suffice, suffuse & suppose"); if you want to see all words that INCLUDE your word, do a Floating Search ("hand" retrieved glad hand, hand-to-hand, deck hand & hand grenade). This is also a dictionary of synonyms.