Firstly -- Kindles recognize the .azw .mobi and .prc file extensions as equivalent. So for the purposes of this discussion, you can forget about the file extension.
Assuming the dictionary is indeed formatted using dictionary markup, which AFAIK hasn't changed since the PRC days anyway, it will work fine. As a security blanket, you can rename it to .mobi -- it can't hurt, you will feel better, and the Kindle will not notice a difference.
If sideloading the dictionary gives you a book instead of a dictionary, then it is useless. You will have to find something else or build your own with mobigen/kindlegen. There are guides to doing that here, starting from a tab-delimited text file. Inflections will have to be added by hand.
calibre cannot help you!! It has no code to handle dictionaries, and will simply convert a dictionary into paged text, which may be readable but certainly won't enable lookups.

Aside: Upgrade calibre, if you have 0.8.51 then you are three major versions and several years out of date.