Cryptic code gains spirit of good manners (7)
I believe the answer is:
decorum
'good manners' is the definition.
(I've seen this before)
'cryptic code gains spirit' is the wordplay.
'cryptic' indicates an anagram (a cryptic or obscure order of the letters).
'gains' is a charade indicator (letters next to each other).
'spirit' becomes 'rum' (alcoholic spirit).
'code' with letters rearranged gives 'deco'.
'deco'+'rum'='DECORUM'
'of' acts as a link.
(Other definitions for decorum that I've seen before include "Good manners" , "(Of outward appearances) what is proper" , "This is becoming" , "Protocol" , "modesty" .)