I agree, the free online dictionaries are not always sufficient. If you're willing to pay for access, I would suggest subscribing to an online dictionary called "Stor engelsk ordbok"/"English Comprehensive Dictionary" from Kunnskapsforlaget (this is a two-way dictionary, Norwegian-English/English-Norwegian).

It's possible to try it out for free (for a period of 15 days) to see if it suits your needs or not.

You can click on "View site in English"/"Se siden på norsk" at the top of the page.

http://www.ordnett.no/butikk/engelskeordbøker.storengelskordbok