Might be a variation of MAESTU or MAEZTU. There is a palace in MAEZTU (Arraia, Alaba) with branches in other parts of Alaba and in Nabarra. On the gates of the Church in San Millán from 1025 it appears in the form BAHAHETZU.

It comes from "areitz" (meaning oak) and the suffix "tu" (meaning abundance). So the original house was probably in an area where there were many oak trees.

The shield is a field of blue with a diagonal stripe of gold going from the top left corner to the bottom right corner and on either end of the stripe is a dragon's head in silver (actually this looks less like a dragon and more like a two headed snake). Also, on the top part there is a "tao" (no idea what this is) and on the bottom part a "flor de lis."