Boringly traditional suit (6)
I believe the answer is:
square
I believe this clue is a double definition.
'boringly traditional' is the first definition.
(I've seen this before)
'suit' is the second definition.
(thesaurus)
(Other definitions for square that I've seen before include "Old fogey" , "Series of steps with four couples" , "Stick-in-the-mud -- quadrangle" , "Londoners associate with Leicester" , "New York Times, for example" .)