It's an area where online dictionaries don't do very well, I'm afraid. www.thesaurus.com has a reasonable antonym feature.
I found a thread on antonyms together with lists of suggestions. Having looked at all the sites mentioned I have to say that I am particularly disappointed; not only is there little offering for antonyms but even quite everyday words were not recognised, e.g. essentially!!
Has anyone found a really good dictionary with a full spresd of antonyms
Thank you for confirming my findings. I thought that I had failed to look hard enough and was missing something. Ah well, back to the library; something I have not had to do since starting to use the web years ago.
Library? I have a vague memory...