A civic dignitary for a month or more? (5)
I believe the answer is:
mayor
'a civic dignitary' is the definition.
(I've seen this before)
'month or more?' is the wordplay.
'month' becomes 'may' (May is an example).
'more?' means one lot of letters go next to another (some letters added to the previous ones).
'may'+'or'='MAYOR'
'for a' is the link.
(Other definitions for mayor that I've seen before include "Town chief" , "Elected city head" , "Head of a city council" , "Civic head of town or borough" , "City government head" .)