Severe blow for hard-headed bachelors (4)

I believe the answer is:

bash

I'm a little stuck... Click here to teach me more about this clue!

'severe blow' is the definition.
'bash' can be an answer for 'blow' (bash is a kind of blow). I am unsure of the 'severe' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for bash that I've seen before include "Party; attempt (slang)" , "Party - punch" , "Hit hard; party (slang)" , "Try - rave-up" , "Party; beat" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app