Book a court before start of session (4)
I believe the answer is:
acts
'book' is the definition.
(book of the Bible)
'a court before start of session' is the wordplay.
'court' becomes 'ct' (abbreviation used in road names).
'before' says to put letters next to each other.
'start of' says to take the initial letters.
The initial letter of 'session' is 's'.
'a'+'ct'+'s'='ACTS'
(Other definitions for acts that I've seen before include "New Testament book immediately following the Gospels" , "Behaves like thespian" , "Dramatic parts" , "Does something" , "Fifth NT book" .)