It helps prevent a cutthroat from being blunt (5)
I believe the answer is:
strop
This might be a double definition.
'it helps prevent a cutthroat from' is the first definition.
The definition suggests a singular noun which matches the answer.
'blunt' is the second definition.
The answer and definition can be both to do with contact as well as being verbs in their base form.
Maybe you can see a link between them that I don't see?
'being' acts as a link.
Can you help me to learn more?
(Other definitions for strop that I've seen before include "temper tantrum" , "Display of temper" , "Piece of leather on which razor is sharpened" , "Paddy" , "Strip of leather on which razor is sharpened" .)