without seeing the bottom I can only be half sure.
But it appears to be a locking batten board. They were mostly used in older sailing ships and Victorian era yachts. To batten down the galley door or a deck hatch in boats. Victorian era parlor panels used them also to link the panels together when they were opened. When the hatch was down it activated a lock at the top of the panel to lock it in place, much like a commercial door with a push bar that locks the door at the top and bottom of the door instead of a jam. Judging my the wear of the teak and the dimensions I would almost be certain.
But without seeing others pics I cannot be certain