Earlier quoted context omitted.
I'm learning Dutch, and it's even worse. Really basic, commonly used words aren't there. Good dictionaries are hard to build. At the same time, the web isn't constrained by space the same way a physical book is, which means that a result should have even more information. You shouldn't accept an online dictionary that gives you only one simple usage of a word. A good dictionary will list the short & sweet definition,…
I'm Dutch, and I use the electronic Van Dale Groot Woordenboek (€99). Google will give you wiktionary for the word "slim" ( http://nl.wikipedia.org/wiki/Slim ) Van Dale gives you this: http://dl.dropbox.com/u/381493/van_dale_slim.jpeg
http://www.mijnwoordenboek.nl/
"Slim" isn't a very good example for that dictionary, but check out something with a lot of possible EN-NL translations, usages, and jargon.
http://www.mijnwoordenboek.nl/vertalen.php?src=NL&des=EN...
That site refers you to "Babylon 8", another installable dictionary which just came out with a Mac version. I'm not sure if it returns the same results as the site, but if it does I'd say it's a pretty good competitor for the VDGW (which is truly fantastic, itself).