Invalidation about to restrict north German city (9)
I believe the answer is:
annulment
'invalidation' is the definition.
(synonyms)
'about to restrict north german city' is the wordplay.
'about' becomes 'anent' (archaic Scottish term).
'to restrict' is an insertion indicator (inserted letters are restricted or contained).
'north' becomes 'N' (abbreviation).
'german city' becomes 'ulm' (Ulm is a city in Germany).
'n'+'ulm'='nulm'
'anent' enclosing 'nulm' is 'ANNULMENT'.
(Other definitions for annulment that I've seen before include "recall" , "Countermand" , "dissolution" , "cancellation" , "Declaration of invalidity, of a marriage say" .)