When I need refer to an English dictionary, I'm often using Oxford Dictionaries( http://www.oxforddictionaries.com/ ) and Cambridge Dictionaries Online( http://dictionary.cambridge.org/ ). I use them mainly in order to distinguish synonyms. But sometimes their illustrative sentences are too abstract and incomprehensive for me. I know I still don't understand some concepts in English which are unfamiliar in Japanese, but at the same time, I suspect that those sites have only insufficient contents for their free usage on the Internet. Is the quality of those sites' contents good for English learners like me?

Thanks to both of your answers!

>joshwhetstone
The site is managed by Oxford University Press. In this site I can see illustrative sentences more if I have got a premium account. I also have an electronic dictionary which contains Oxford Advanced Lerner's Dictionary 7th edition, but this doesn't have so many illustive sentences(an English-Japanese dictionary in it seems to have more sentences than it). So I have not known how many illustive sentences really there are in Oxford English Dictionary.

>elise
In this site I can see plenty of synonyms with the difference among them in addtion to illustraive sentences. It can provide me with what I want to know, so I try to use it.

I have not known that Oxford Dictionary is different from the Lerner's Dictionary! Thank you very much.

Oops I've mistyped.. Thanks.