If you are using ZBedic or QBedic then you don't need to decompress. Both of these systems will decompress the dictionary on the fly.
If you are using something else then be aware that this dictionary is in a format targetting these two readers... you can, however, decompress to see the raw data using gzip -d (If you are doing this from M$ Win with WinZip then rename to .gz and WinZip will see the association).
- Andy