I would like to use a monolingual japanese dictionary in rikaichan (or rikaisama), but I can not find a free one.
I have read that 明鏡 is quite good, but is it free?
Where can I download it?
I have already searched in the forum, but I can not find download links.

I can also buy one, but I have to be sure that it works with rikaichan.
Can you suggest me some good links?

Thanks in advance.

Can you use websites? If so,
http://dic.yahoo.co.jp/
is pretty good, though it may show some rare readings of kanji; for instance, 役 has three different entries depending on reading, and only one of them is common.

If you press O in Rikaisama, it fetches monolingual definitions from 三省堂. They're pretty good. No download required (but doesn't work offline).

You definitely won't find anything if you search this forum for "EPWing download".

Googling random words like "rutracker epwing" won't get you anywhere. *wink*

As for monolingual dictionaries, the most common ones are Dajisen, Daijirin, Koujien, and Meikyou. I think Meikyou is the easiest. I usually use Meikyou and Daijisen, though I use them all a lot. You might want to check out here for more info on certain dictionaries.