Dissolute rake seized by school head — odd character! (12)
I believe the answer is:
freakishness
'odd character' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'dissolute rake seized by school head' is the wordplay.
'dissolute' indicates an anagram.
'seized' indicates putting letters inside.
'by school' becomes 'fish' (group of fishes. I am not sure about the 'by' bit.).
'head' becomes 'ness' (both can mean a promontory).
'rake' with letters rearranged gives 'reak'.
'reak' put inside 'fish' is 'freakish'.
'freakish'+'ness'='FREAKISHNESS'
Can you help me to learn more?