Cut off from rum cove's back earlier (8)
I believe the answer is:
estrange
'cut off' is the definition.
(thesaurus)
'rum cove's back earlier' is the wordplay.
'rum' becomes 'strange' ('strange' can be a synonym of 'rum').
'cove's back' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'earlier' is a charade indicator (letters next to each other).
'strange' after 'e' is 'ESTRANGE'.
'from' acts as a link.
(Other definitions for estrange that I've seen before include "disunity" , "Lose friendship" , "separate" , "split up?" , "Become unfriendly towards sergeant" .)