First section of novel copper initially labelled as rather peculiar (10)
I believe the answer is:
particular
'peculiar' is the definition.
(synonyms)
'first section of novel copper initially labelled as rather' is the wordplay.
'first section of novel' becomes 'Part I' (first part of a novel).
'copper' becomes 'cu' (chemical symbol).
'initially' indicates taking the first letters.
The initial letters of 'labelled as rather' is 'lar'.
'parti'+'cu'+'lar'='PARTICULAR'
(Other definitions for particular that I've seen before include "Meticulous" , "Specific" , "Fastidious; individual" , "going into detail" , "Fussy" .)