Hi Myle,
I heard someone managed to run some dictionaries like Merriam Webster using wine, but... installing it on a windows partition though, if I'm not mistaken. Anyway, I'm not sure how they would work... try searching the net for someone who succeeded.
You could get the major dictionaries as files for Stardict, for example but... when I tried it, I couldn't find the pronunciations in them, not even phonetic transcriptions... just the contents.
So it seems to me there are no good dictionaries for the penguin... and so what do I do? I use online dictionaries. All the best ones are available online and for free.
Lemme know...