What is this piece slightly longer than a 2x2 plate with grooves and a hole? Once again, I need the collective wisdom of this group to identify a mystery LEGO element! 

I did a search for "2x2"and went through scores of Bricklink pages, but I couldn't find this particular piece. 

It's the size of a 2x2 plate, but with this added grooved part that I've never seen before.
This looks like a PLATE 2X2 ANGLE, which is broken. There is a rough side shown on the picture.