Disengage and go very bitter (8)
I believe the answer is:
freezing
'bitter' is the definition.
(thesaurus)
'disengage and go' is the wordplay.
'disengage' becomes 'free' (synonyms).
'and' says to put letters next to each other.
'go' becomes 'zing' (I've seen this before).
'free'+'zing'='FREEZING'
'very' acts as a link.
(Other definitions for freezing that I've seen before include "Changing to ice" , "suffering from cold" , "Turning to ice" , "Like ice" , "Ice-cold" .)