Male with cunning thought sincere (9)
I believe the answer is:
heartfelt
'sincere' is the definition.
('heartfelt' can be similar in meaning to 'sincere')
'male with cunning thought' is the wordplay.
'male' becomes 'he'.
'with' means one lot of letters go next to another.
'cunning' becomes 'art' (I've seen this before).
'thought' becomes 'felt' (feeling is a kind of thinking**).
'he'+'art'+'felt'='HEARTFELT'
(Other definitions for heartfelt that I've seen before include "Kindly" , "Sincerely intended with strong feeling" , "Let father have deep and earnest kind of emotion (9)" , "Most fervent in cardiac way" , "unfeigned sincerity" .)