Blue dressing is cut off (6)
I believe the answer is:
disown
'cut off' is the definition.
(thesaurus)
'blue dressing is' is the wordplay.
'blue' becomes 'down' (I've seen this before).
'dressing' means one lot of letters goes inside another (a dressing is a kind of covering).
'down' placed around 'is' is 'DISOWN'.
(Other definitions for disown that I've seen before include "Refuse to be associated with (something/someone)" , "Refuse responsibility for" , "Reject all connection or relationship with" , "Deny any connection with" , "Repudiate, disclaim" .)