The old man going to court to secure agreement (4)
I believe the answer is:
pact
'agreement' is the definition.
(a pact is an agreement or deal)
'the old man going to court' is the wordplay.
'the old man' becomes 'pa' (both can mean someone's father).
'going to' means one lot of letters go next to another.
'court' becomes 'ct' (abbreviation used in road names).
'pa'+'ct'='PACT'
'to secure' acts as a link.
(Other definitions for pact that I've seen before include "Alliance" , "Settlement" , "Agreement, bargain" , "International treaty" , "Treaty, formal agreement" .)