There's an inbuilt dictionary in the Kindle. You move the curser to the word and an explanation shows up. There have been a few issues with translation dictionaries though, as it appears that the Kindle couldn't handle other input languages than English - but it should be fixable - see this thread from post #29 and onward:
https://www.mobileread.com/forums/sho...t=60103&page=2
Edit, added: there's another solution - see same thread as linked to above, post #53
But I think that there's now a larger variety of deafult dictionaries available for the Kindle. You can have a look at Amazon to see what is avaliable. Remember, it must be a Kindle
default dictionay.