I have to same most people here seem to think atemi is a punch in the head or a kick to the 'nuts' but osensei said atemi is 70(to 99)% aikido for a reason. Which is (since aikido is related to kenjutsu) we use our tegatana to atemi in EVERY technique, do you not take uke down with your tegatana in irimi nage, and do you not cut down in both shiho nage and ude osae with your tegatana, these are atemi. A quote from Gozo Shioda, "The moment of contact becomes the strike." and "If you make contact with uke with focused power, that is atemi, so it is possible to use your shoulder , your back, or any part of your body to make atemi."
There you go hope it helps some people.