A plot-bunny (idea for a story), especially one related to The Lord of the Rings. Originated at OFUM
. It takes the form of a 'bunny' because of its resemblance to the Norwegian word for 'soft'.
"Nuzgul" originated as a mini-Balrog
misspelling of "Nazgul," the undead Ring-wraiths from Tolkien's Middle-earth, but soon developed its own meaning.