I've got Volume IX of the OED sitting on my lap as I write this.

Yes, "materteral - adj - characteristic of an aunt" is in here.

From Latin matertera, maternal aunt.

In the same entry it lists "materterine -adj" as meaning the same thing..

Now I suggest we start a new discussion about the phrase "dollars to donuts/doughnuts". (I'd never heard that one before.)

pieman