To clarify, it is not the total number of words but rather the number of unique words considered. Imho a million of unique words is okay. A bigger concern for me would be that words on Wikipedia can be overly specific.
Have you considered a similarity search approach? They would handle your oddly specific synonym issue
I only have a prespellechecked list of words from here: http://www.aaabbb.de/WordList/WordList_en.php