OneLook Dictionaries Searches
various specialized dictionaries, and then
organizes their results, so that the user
can choose the context in which the word is
to be defined.
The Wordsmyth English Dictionary-Thesaurus (WEDT) A full
dictionary and a complete thesaurus,
integrated into one work; you only need to
look up a word once, with hyperlinks to
synonyms, and similar or related words
available where appropriate.
what?is.com Specialized
dictionary on Information Technology, and
explains the meaning of words, but also
includes concepts and phrases.