[RubyR]

More on “Toot”. Apparently his it is a nickname for his grandmother.

http://www.suntimes.com/news/politics/obama/familytree/545449,BSX-News-wotreeee09.stng
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Her name is Madelyn Payne Dunham, but to Obama she was always “Toot,” a shortened version of Tutu, a Hawaiian word for grandmother or older female relative.

[usmcobra]

I think since there was a "Anna Toot" in his family tree it is much more then a shorten version of hawaiian for old lady or Grandma. His mother's family moved to Hawaii only a couple of years before Obama was born so that natural Hawaiian heritage just isn't there.

I say that after reading that article Obama assumes that the root of the nickname is Hawaiian.

What Toot believed kept her going were the needs of her grandchildren and the stoicism of her ancestors," Obama wrote.

"Anna Toot" whoever she was, was someone his mother and his grandmother knew of and admired enough to take her name as their own, to the extent that his mother was known by that name by her African In Laws and his grandmother preferred to be called by it.