[KevinH]

Do not edit the .dic file. Edit the .aff file if you want to remove the period from acceptable wordchars.

And to answer your question, those are affix and suffix flags that specify which affixes or suffixes are valid with that root word. The .dic file lists root words with affixes that are allowed instead of every possible word. Those affix flags are of course defined in the .aff file. A dictionary made of a simple wordlist is unworkable for many languages due to compound words and compound affixes and suffixes. So to shrink its size to reasonable levels the dictionary must use some form of affix compression.

I you want to add words, do it to a Sigil wordlist (you can create and select them easily in Sigil). See the Spellcheck discussion in the Sigil User guide for more info. You can use the default or make one specific for your current epub.

Why on earth are you trying to edit words inside the .dic files?

If you truly need to change what words are legal then use the tools in Hunspell to expand the .dic file properly into a wordlist, make changes, then re-affix compress that huge wordlist file to create what a new .dic file.

Google "affix compression"