Author may start a new line (5)
I believe the answer is:
milne
'author' is the definition.
(I know that Milne is a author)
'may start a new line' is the wordplay.
'start' says to take the initial letters.
'a new' indicates an anagram.
The initial letter of 'may' is 'm'.
'line' is an anagram of 'ilne'.
'm'+'ilne'='MILNE'
(Other definitions for milne that I've seen before include "A.A. -, Pooh author" , "Pooh's creator" , "Children's author" , "Writer of Winnie the Pooh" , "A.A. --, Pooh creator" .)