You can't copyright a name IIRC, but you can trade mark it. To qualify under the copyright rules it has to show sufficient skill and expertise in its creation, a name is too short and random. You can't use the description though, this would be pushing it I think. Best thing to do is ask for permission from JK Rowling's agent (good luck with this!).
I have started writing down my experiences of domestic abuse...at first it was purely for my own therapy but actually I'm thinking of putting it into book form and getting my side of the story out (I was denied my say in court as the trial collapsed). Myself and the DC have never referred to HIM by his name, he has always been called 'the dementor' after the character in Harry Potter. I want to call the book 'The Dementor' and refer to him throughout the book as that. Also quote JK Rowling's description of the dementor.
So...would I need permission to do this? Are characters covered by copyright?