Account held in part agreement (4)
I believe the answer is:
pact
'agreement' is the definition.
(pact is a kind of agreement)
'account held in part' is the wordplay.
'account' becomes 'ac'.
'held in' indicates putting letters inside.
'part' becomes 'pt' (I've seen this in other clues**).
'ac' inserted within 'pt' is 'PACT'.
(Other definitions for pact that I've seen before include "deal" , "Settlement" , "Alliance" , "Formal agreement between parties or states" , "Written agreement between two states" .)