Rash unacceptable escape (8)
I believe the answer is:
outbreak
'rash' is the definition.
(thesaurus)
'unacceptable escape' is the wordplay.
'unacceptable' becomes 'out' (I've seen this in other clues).
'escape' becomes 'break' (break is a kind of escape).
'out'+'break'='OUTBREAK'
(Other definitions for outbreak that I've seen before include "Sudden onset (of war, disease, etc)" , "Onset -- epidemic" , "Eruption of e.g. disease" , "Sudden start" , "disturbance" .)