"A Book of Nonsense" author (4)
I believe the answer is:
lear
'a book of nonsense author' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lear that I've seen before include "of poetry?" , "Humorist, Edward --" , "tragic figure" , "Tragic Shakespearean king" , "A real playful king" .)