Word Dictionary dialog box (Tools | Word Dictionary... menu) is used to add/delete/browse the words in the dictionary. You may build your own word dictionary by adding words from your existing documents.
Word dictionary is used in the auto completion and word check functions. (BarahaPad also uses downloaded files containing word lists during the word-check process.)
You may add frequently used long words to the dictionary. They will be shown in the auto completion box.

Word:
Type word to search in dictionary
Matching words:
Lists words from dictionary that begin with text typed in "Word" box
Add:
Adds word typed in "Word" box to dictionary
Delete:
Deletes word typed in "Word" box from dictionary
Add All Words:
Adds all words from current document to dictionary
Delete All Words:
Deletes all words from dictionary