Humiliate Hebridean island in terrible mess (9)
I believe the answer is:
embarrass
'humiliate' is the definition.
(I've seen this in another clue)
'hebridean island in terrible mess' is the wordplay.
'hebridean island' becomes 'barra' (I've seen this before).
'in' means one lot of letters goes inside another.
'terrible' indicates an anagram.
'mess' is an anagram of 'emss'.
'barra' put inside 'emss' is 'EMBARRASS'.
(Other definitions for embarrass that I've seen before include "Show up" , "Make uncomfortable" , "Cause (someone) to feel awkward" , "Encumber" , "Discomfit" .)