Novel written in one week (3)
I believe the answer is:
new
'novel' is the definition.
(synonyms)
'written in one week' is the wordplay.
'written in' indicates the answer is hidden within the clue.
'NEW' is hidden within 'one week'.
(Other definitions for new that I've seen before include "'Fresh, novel (3)'" , "Original" , "Novel, recent" , "Not previously used" , "Unconventional" .)