Stiffness of manner, formality (6)
I believe the answer is:
starch
I believe this is a double definition.
'stiffness of manner' is the first definition.
(I've seen this before)
'formality' is the second definition.
(being excessively formal or stiff)
(Other definitions for starch that I've seen before include "Stiffener in the laundry" , "Carbohydrate found in potatoes, wheat etc." , "Stiffening preparation used in laundering" , "Stuff that stiffens, say collars" , "Stiffening carbohydrate" .)