I've just come across this delightful online dictionary.
It seems to anticipate your requirements as you type into it.
As well as a "classical" English dictionary it has the "Free Online Dictionary of Computer Terms", a database on the Elements of the Periodic Table, a thesaurus and an English-Japanese translation tool. I'm not quite sure exactly how that works but it sounds intriquing.
Update from The Outback: Parts 1 and 2
2 hours ago