Below are some common Japanese expressions Aikidoists commonly use in class when practicing. A more detailed glossary of Japanese terms, attacks and defences, can be found in the Vancouver Aikikai Intro to Aikido Beginners Document.
Onegai shimasu (Please share with me)
This is said to Sensei at the beginning of class, after he/she gives instruction to the entire class or when you ask him/her for help. You also say this to your partner before practicing a technique.
Domo Arigato gozaimashita (Thank you very much)
This is said to Sensei if he/she has given you personal instruction during class and to Sensei at the end of class. It is said to your partner after practicing a technique and to all partners at the end of practice.
Sumimasen (I’m sorry / Excuse me)
Accompanied by a bow, this is said to another practitioner or couple when you accidentally bump them or to your partner when you make a mistake.