Is he nothing but a blemish? (5)
I believe the answer is:
oscar
'is he nothing' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'but a blemish?' is the wordplay.
'but' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'a blemish?' becomes 'scar' (I've seen this before).
'o'+'scar'='OSCAR'
Can you help me to learn more?
(Other definitions for oscar that I've seen before include "Librettist Hammerstein, d. 1960" , "Annual film award" , "academy's prize" , "Film prize" , "Phonetic code for O" .)