Around six fifty, complain (5)
I believe the answer is:
cavil
'complain' is the definition.
(thesaurus)
'around six fifty' is the wordplay.
'around' becomes 'ca' (circa).
'six' becomes 'vi' ('vi' can be a synonym of 'six').
'fifty' becomes 'l' ('L' can be a synonym of 'fifty').
'ca'+'vi'+'l'='CAVIL'
(Other definitions for cavil that I've seen before include "Minor complaint" , "Find fault" , "Make trivial objection" , "Quibble" , "Make petty objections" .)