In Hawaiian : 
Grandmother - Tutu Wahine (Whahine being woman)
Grandfather - Tutu Kane (Kane - means man or male)
Both shortened to Tutu if just one present. 
Wahine = Wha-he-nay
Kane = khan-ay
My maternal Grantparents were Gramma and Grampa.
My father's parents died when Dad was 12 so no confusion.
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Note: To be absolutely correct tutu is really kuku but prononced and generally written as tutu (too-too) The definitave Pukui Elbert Hawaiian Dictionary notes this is apparently a "new" word as it is not found in the ancient Hawaian chants. 
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A friend's grandchildren call her Nana.