The Latin suffix -ion, is meant to show that an action is being initiated or a condition is being felt. They are mostly used to form past participles such as creation and allusion.
In the words confusion and suspicion, the presence of the ion there is meant to covey that the subject is experiencing the condition of being confused or suspicious.
This quote can be found only in the movie. It can be heard in the third movie, and is told by the headmaster. I just checked the book, and it doesn't appear there.
