Part of centre-page spread (10)
I believe the answer is:
percentage
'part' is the definition.
('percentage' can be a synonym of 'part')
'centre-page spread' is the wordplay.
'spread' indicates anagramming the letters.
'centre'+'page'='centrepage'
'centrepage' anagrammed gives 'PERCENTAGE'.
'of' acts as a link.
(Other definitions for percentage that I've seen before include "Maybe commission" , "Proportion stated in hundredth parts" , "Proportion in each 100" , "Proportion, share" , "cut?" .)