The word "nana" for grandma is probably of baby-talk origin. It could also came from the Italian word for grandmother which is "nonna".
On the other hand, although papa is sometimes used for grandfather/grandpa, it is often address to as "father". The word papa is Apalaí, a Cariban language spoken in Brazil.
The table below shows different forms used for mother and father.
Learn more on where 'nana' and 'papa' came from at University of Sussex.
Tip! Choosing a grandparent name is a more complicated task than it might seem. Get help in finding the perfect grandparents name at About.com.