A small volume employed for defendant (7)
I believe the answer is:
accused
'defendant' is the definition.
(synonyms)
'a small volume employed' is the wordplay.
'small volume' becomes 'cc' (cubic centimetre).
'employed' becomes 'used' ('use' can be a synonym of 'employ').
'a'+'cc'+'used'='ACCUSED'
'for' acts as a link.
(Other definitions for accused that I've seen before include "Incriminated" , "Levelled a charge against" , "Indicted" , "Blamed" , "Defendant in a criminal proceeding" .)