Subdued, thanks to me, on the first of December (5)
I believe the answer is:
tamed
'subdued' is the definition.
('tame' can be a synonym of 'subdue')
'thanks to me on the first of december' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'on' is a charade indicator (letters next to each other).
'the first of december' becomes 'd' (1st letter of 'december').
'ta'+'me'+'d'='TAMED'
(Other definitions for tamed that I've seen before include "Of animals, domesticated" , "Reined" , "now behaving himself?" , "Domesticated or subdued" .)