Declaring French port bust (6)
I believe the answer is:
breast
'bust' is the definition.
(I've seen this before)
'declaring french port' is the wordplay.
'declaring' shows a homophone (sound like) (I've seen 'declare' mean this).
'french port' becomes 'brest' (port city in Brittany).
'brest' sounds like 'BREAST'.
(Other definitions for breast that I've seen before include "joint for diners" , "flesh" , "Outstanding feature" , "Milk supplier" , "boob" .)