Shared amount buyable: odd bits have been excluded (6)
I believe the answer is:
mutual
'shared' is the definition.
(similar in meaning)
'amount buyable odd bits have been excluded' is the wordplay.
'amount' becomes 'mut' (mut is a kind of amount).
'odd bits have been excluded' indicates alternate letters (letters in odd-numbered positions removed).
The alternating letters of 'buyable' are 'ual'.
'mut'+'ual'='MUTUAL'
(Other definitions for mutual that I've seen before include "Joint < commonly" , "Felt by each towards the other, like friendship" , "Affecting both parties" , "building society, say" , "Dickens novel 'Our . . . . . . Friend'" .)