mirthless

Black started to laugh, a horrible, mirthless laugh that filled the whole room.

It was a grating unpleasant laugh, not only mirthless, but meaningless.

It was a curious laugh; distinct, formal, mirthless.

Wormtail muttered something so quietly that Frank could not hear it, but it made the second man laugh -- an entirely mirthless laugh, cold as his speech.

And still, Voldemort and Harry looked at each other, and now Voldemort tilted his head a little to the side, considering the boy standing before him, and a singularly mirthless smile curled the lipless mouth.