This is an English dictionary for spell checking purposes - basically just a list of words, in text format.  Note that this must be sorted in order for spell checking to work.  SlyEdit's new spell checker feature, for instance, uses a binary search with an array of words loaded from a dictionary to check the validity of words.
SlyEdit's new spell check feature assumes dictionary filenames are dictionary_<language>.txt, where <language> is the language name.