Stop key piercing skin (7)
I believe the answer is:
rescind
'stop' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how they can define each other.
'key piercing skin' is the wordplay.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'piercing' means one lot of letters goes inside another (some letters pierce a hole in others).
'skin' becomes 'rind' (synonyms).
'esc' placed within 'rind' is 'RESCIND'.
Can you help me to learn more?
(Other definitions for rescind that I've seen before include "Set aside law" , "Revoke (a law/order)" , "Quash" , "Annul - discern (anag)" , "Cinders (anag.)" .)