Home Secretary defends weapon that causes injury (5)
I believe the answer is:
harms
'causes injury' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot see how they can define each other.
'home secretary defends weapon' is the wordplay.
'home secretary' becomes 'hs' (this could be a standard abbreviation which I don't know about).
'defends' is an insertion indicator.
'weapon' becomes 'arm' ('arm' can be a synonym of 'weapon').
'hs' going around 'arm' is 'HARMS'.
'that' is the link.
Can you help me to learn more?
(Other definitions for harms that I've seen before include "Injures, damages" , "Wounds" , "Hurts, damages" .)