Chap with assignation getting authority (7)
I believe the answer is:
mandate
'authority' is the definition.
(thesaurus)
'chap with assignation' is the wordplay.
'chap' becomes 'man' (I've seen this before).
'with' says to put letters next to each other.
'assignation' becomes 'date' (I've seen this before).
'man'+'date'='MANDATE'
'getting' acts as a link.
(Other definitions for mandate that I've seen before include "approval" , "Authorization, official instruction" , "Official order or commission to do something" , "Give authority to" , "Authority conferred on a tandem" .)