Recognised a sound novel (4)
I believe the answer is:
knew
'recognised' is the definition.
(know can mean to recognise someone)
'a sound novel' is the wordplay.
'a sound' indicates a 'sounds like' (homophone) clue.
'novel' becomes 'new' (synonyms).
'new' is a homophone of 'KNEW'.
(Other definitions for knew that I've seen before include "Had learnt; sounds like modern" , "Was cognizant of" , "Distinguished" , "Was familiar with" , "Was cognisant or aware of" .)