boggart
A shapeshifting monster that feeds on fear.
"A boogeyman," I said. "Sometimes known as a boggle or a boggart. It's a weak form of phobophage - a fear-eater, mostly insubstantial."
Where it comes from
Variant of boggard, recorded since 18th century. As a monster that feeds on fear, coined by British novelist J. K. Rowling in 1999 in Harry Potter and the Prisoner of Azkaban.
Adapted from the Wiktionary entry boggart (CC BY-SA 4.0).