Awfully rude about firm -- Master requires propriety (7)
I believe the answer is:
decorum
'propriety' is the definition.
(I've seen this before)
'awfully rude about firm master' is the wordplay.
'awfully' indicates an anagram.
'about' is an insertion indicator.
'firm' becomes 'co' (a firm is a company).
'master' becomes 'm'.
'rude' with letters rearranged gives 'deru'.
'deru' placed around 'co' is 'decoru'.
'decoru'+'m'='DECORUM'
'requires' is the link.
(Other definitions for decorum that I've seen before include "Decency" , "Good manners" , "modesty" , "Dignity of behaviour or procedure" , "This is becoming" .)