They say to make firm declaration (13)
I believe the answer is:
pronouncement
'declaration' is the definition.
(pronouncement is a kind of declaration)
'they say to make firm' is the wordplay.
'they say' becomes 'pronoun' ('they' is a pronoun).
'to make firm' becomes 'cement' (I've seen this in another clue).
'pronoun'+'cement'='PRONOUNCEMENT'
(Other definitions for pronouncement that I've seen before include "ordinance" , "Official declaration" , "formal statement" , "official statement" , "An authoritative declaration" .)