So I recently stumbled on a feat called Bounding Hammer. As it states
Benefit: As a standard action, you may throw a hammer at an opponent within 20 feet. If you hit (whether or not the attack damages the target), the hammer rebounds off of the creature and lands in your square. If you have the Snatch Arrows feat, you may choose to catch the hammer when it enters your square (though this does not give you the ability to immediately throw the hammer). This ability may not work against some creatures or in certain circumstances as determined by the GM; for example, your weapon does not bounce off Incorporeal creatures (unless it has the ghost touch ability), it may stick to creatures with the adhesive ability, the slowing effect of fighting underwater prevents you from using this feat, and so on.
So with that said I'm not sure how to define a hammer. Do you go by typical hammer or does it include anything that is called a hammer (for instance a Meteor Hammer), but looks nothing like a hammer.
Now the reason I question this is because of racial weapons like the elven curve blade, or a dwarven war hammer. Both races get a racial bonus stating that they treat any weapons with their respective name in the title as a martial weapon.
However it seems against the spirit of the feat to use it on a weapon that in no way shape or form resembles what you'd picture as a hammer.
Best Answer
For such a definition I would look at the Hammer weapon group for the fighter. The one on archives of Nethys reads:
There is an updated version of the weapon groups in a blog on the Paizo forums. It reads:
Not directly on topic but for throwing the two-handed hammers look at the two-handed thrower feat.