Hi nivedita, actually in India, the difference between both these terms is very thin, as many times you would see dieticians refering themselves as nutritionist, and vice-versa. but if you actually compare, a dietican is more qualified person in terms of training and acedemics.
The title "Registered Dietitian" is protected by Law -- so that only qualified practitioners who have met education qualifications can use that title. They are the members of the "indian dietetic association". A dietitian is a health professional who has a Bachelor's degree, specializing in foods and nutrition, or clinical nutrition as well as a period of practical training in a hospital or community setting. Many dietitians further their knowledge by pursuing a Master's or Doctoral degree.
The term Nutritionist is not protected by law in all provinces so people with different levels of training and knowledge can all themselves a "Nutritionist". there are some 6 monthly or 1 yearly certificate courses in food science and nutrition. such people can refer to themselves as nutritionist , they dont necesarrily have a hospital training.