Outspoken old man in Paris is to marry (4)
I believe the answer is:
pair
'is to marry' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pair that I've seen before include "Couple - wed" , "Agreement to avoid division" , "Put together - two of a kind" , "E.g. two aces; mate" , "Brace, couple" .)