Contract to provide half of Oxford with a small volume (6)
I believe the answer is:
accord
'contract' is the definition.
(thesaurus)
'half of oxford with a small volume' is the wordplay.
'half of' means to take half the letters.
'with' means one lot of letters go next to another.
'small volume' becomes 'cc' (cubic centimetre).
'oxford' cut in half is 'ord'.
'a'+'cc'='acc'
'ord' after 'acc' is 'ACCORD'.
'to provide' acts as a link.
(Other definitions for accord that I've seen before include "binding agreement" , "Agreement - conformity" , "Consent or agreement" , "Harmonize" , "Unanimity" .)