Best bra designed by individual to show bit of chest (10)
I believe the answer is:
breastbone
'bit of chest' is the definition.
('breastbone' is part of 'chest')
'best bra designed by individual' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'by' means one lot of letters go next to another.
'individual' becomes 'one' (an individual is one person).
'best'+'bra'='bestbra'
'bestbra' with letters rearranged gives 'breastb'.
'breastb'+'one'='BREASTBONE'
'to show' acts as a link.
(Other definitions for breastbone that I've seen before include "Rib neighbour" , "Sternum" .)