Reveal part of big number (9)
I believe the answer is:
showpiece
'big number' is the definition.
'reveal part' is the wordplay.
'reveal' becomes 'show' (synonyms).
'part' becomes 'piece' (piece is a kind of part).
'show'+'piece'='SHOWPIECE'
'of' acts as a link.
(Other definitions for showpiece that I've seen before include "shining example" , "Outstanding item" , "Impressive exhibit" , "fine specimen of its kind" , "flagship" .)