Dear all,
Just to clarify, I have no problem at all with you using the Cambridge, Macmillan, Collins or Oxford dictionaries. I don’t even have problems with leo.org or dict.cc, depending on what it is you want to do. I use them in my classes sometimes, they are very useful. (Same goes for Wikipedia etc.)
What I don’t like is when people quote englischhilfen.de or some other website that targets learners of English as a foreign language in their term papers – unless it’s a term paper on didactics.
There are two main reasons for that. The first reason is that these pages are very often guilty of didactic oversimplification – they want to make you feel good by giving you simple rules that can easily be shown to be false or at least incomplete. (We’ll do that next semester.)
The second reason is that by quoting (and citing) such sources, you downgrade your paper from a linguistic investigation to the discussion of a personal learner problem. You don’t want to suggest to the reader that you’re still struggling with the English language and that this is your motivation for writing your paper. (So don’t start your papers with “Many learners have problems with…” or “As a prospective teacher, I really need a profound understanding of English grammar”, either.) In a linguistic paper, you should at least pretend that you’re genuinely interested in investigating language. For its own sake.
So, in a nutshell, please use any proper dictionary you like that suits your purpose.