An Exclude dictionary is used to 'remove' words from the main dictionary. A typical example might be to enforce the use of one of two correct alternative spellings e.g. 'customise' and 'customize', by adding the unwanted spelling to the dictionary -
https://support.office.com/en-gb/art...b-3747534edeec
Note that this has little if anything to do with this very old thread. It is much better to create new questions than add to old irrelevant ones.