As HarryT said, which dictionary are you trying to use?
It is possible to convert a tabbed list, but it doesn't handle inflections, as I linked to in your previous thread about dictionaries.
This thread explains the issue:
https://www.mobileread.com/forums/showthread.php?t=20994 Having looked up more info this time
it turns out you may be better off converting something in an XML that the Mobipocket tool understands, like the sample in that link.
This may very well turn out to be a downright project.