OK, never mind. I don't have the time or energy to build this, but maybe one of you can. And earn billions of dollars:
Dictionellisense: Type the beginning of a word in Word , press CTRL+SPACE and have a list of words starting with that word appear and let you choose one.
Press CTRL+SHIFT+SPACE and you'll see a list of synonyms for that word.
IDEs do it. Mobile telephones do it (T9). Even some text editors do it. Why isn't Word?