Closure has a few definitions that don't apply to emotional distress. Such as the closure of a factory or business, in that the word indicates the permanent closing of that entity. As far as the emotional meanings of the word, personally I wouldn't discount the validity of the word. I have experienced what I would call closure to a situation. In that it was an emotionally distressing scenario that my thoughts and actions focused on for a period of time, and when I was able to clear my head of what was lingering and close the doors on that chapter of life.