Dwarvish = resembling Dwarves, of or like the Dwarves. Dwarvish countenance, Dwarvish songs.
Dwarven = member of the Dwarf race or belonging to a Dwarf. Dwarven craftsman, Dwarven halls.
Similarly, Elvish and Elven.
Dwarvenian/Dwarvanist - following the teachings of dwarves... :~D