"The Night Circus" author Morgenstern (4)
I believe the answer is:
erin
'the night circus author morgenstern' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for erin that I've seen before include "Old Ireland" , "'Come back to ...' (emigrant song)" , "Romantic, archaic name for Ireland" , "The Emerald Isle, in poetry" , "Poetically, Ireland" .)