Sets of nine repairing sedan around a corner (7)
I believe the answer is:
enneads
'sets of nine' is the definition.
'repairing sedan around a corner' is the wordplay.
'repairing' indicates an anagram (I've seen 'repair' mean this).
'around' is an insertion indicator.
'a corner' becomes 'ne' (I can't explain this - if you can you should give a lot more credence to this answer).
'sedan' anagrammed gives 'enads'.
'enads' enclosing 'ne' is 'ENNEADS'.
Can you help me to learn more?
(Other definitions for enneads that I've seen before include "Groups with members one over the eight" , "Eights plus coxes, perhaps" , "groups of nine" , "Groups appearing one over the eight" , "Sane end (anag.)" .)