Eering!
What's the one place we should have looked first? Child of course!
It is an archaic word for ploughing and occurs in the blackletter broadside version of The Elfin Knight v12 'For thou must eare it with thy horn' and I'm pretty certain that's where Peter will have found it. He had access to early broadsides and frequently used them in his own concoctions. He was taking a leaf out of Dalrymple's book and what he did with Edward.