1. to hammer a dent away; to make a dent even with the surrounding surface.
> I'm going to have to have someone hammer this dent in my fender out.

2. to expand something by hammering it thinner.
> He hammered the gold out into a very thin sheet.
> He hammered out the gold into thin sheets.

3. to arrive at an agreement through argument and negotiation.
> The two parties could not hammer a contract out.

4. to play something on the piano.
> She hammered the song out loudly and without feeling.