Answer:

ghostwrite

Answer	Crossword Clue
GHOSTWRITE	Compose for another
GHOSTWRITE	Take cash but not credit?
GHOSTWRITE	Do a behind-the-scenes job

GHOSTWRITE	Author anonymously
GHOSTWRITE	Pen, but not for credit
GHOSTWRITE	Work behind the scenes, in a way
GHOSTWRITE	Be a secret author
GHOSTWRITE	Author without credit
GHOSTWRITE	Collaborate with a spook
GHOSTWRITE	Pen for no credit