Cambridge Dictionary
Based on the Cambridge International Corpus, the definitions are mostly taken from the Cambridge Advanced Learner's Dictionary or the Cambridge Learner's Dictionary. The definitions also give you the option of seeing the word in phonetics to help with pronunciation. You can buy the range of Cambridge Dictionaries from ELB.

Hyperdictionary
An online dictionary resource from Hyperdictionary.com . Entering a word in the box opposite will search the online English dictionary and bring you a definition in a pop-up window. Visit http://www.hyperdictionary.com to use their online medical, technical and computing dictionaries as well as the online thesaurus.

Technical Dictionary
A specialised dictionary of Technical English covering computer, Internet and telecommunications terms, acronyms, emoticons or smilies, chat abbreviations, filename extensions, HTML tags, and domain suffixes.

Computing Dictionary
A useful online dictionary and search engine for computer and Internet technology definitions. Regularly updated and with 'term of the day' and 'new terms' features. The definition provided will also give a list of related terms with links to explore further. There is also a pronunciation guide.

Medical Dictionary
Comprehensive medical resource with definitions providing extensive links and avenues for further research. When you input a word, a new window will open - scroll past the sponsored links to get to the definitions and related explanations.