Hard at The Centre not to take advantage of partner - the one who shares (9)
I believe the answer is:
housemate
'one who shares' is the definition.
I know nothing about this answer so I can't tell whether this works.
'hard at the centre not to take advantage of partner' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'at the centre' says to take the centre.
'to take advantage of' becomes 'use' (I've seen this in another clue).
'partner' becomes 'mate' (synonyms).
The central letter of 'not' is 'o'.
'h'+'o'+'use'+'mate'='HOUSEMATE'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for housemate that I've seen before include "One who shares a residence" , "Co-tenant" , "One sharing accommodation" , "person to live with" .)