Ended nice novel welcoming writer's lack of constraint (12)
I believe the answer is:
independence
'lack of constraint' is the definition.
'independence' can be an answer for 'constraint' (thesaurus). I'm not sure about the 'lack of' bit.
'ended nice novel welcoming writer's' is the wordplay.
'novel' indicates anagramming the letters.
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'writer' becomes 'pen' (I've seen this before).
'ended'+'nice'='endednice'
'endednice' anagrammed gives 'indedence'.
'indedence' going around 'pen' is 'INDEPENDENCE'.
Can you help me to learn more?
(Other definitions for independence that I've seen before include "Freedom from outside control" , "Autonomy" , "lack of bias" , "State of relying only on oneself" , "Self-reliance" .)