… mean the end of one nasty medical procedure (5)
I believe the answer is:
enema
'medical procedure' is the definition.
(I've seen this before)
'mean the end of one nasty' is the wordplay.
'end of' indicates one should take the final letters.
'one nasty' is an anagram indicator.
The final letter of 'the' is 'e'.
'mean'+'e'='meane'
'meane' with letters rearranged gives 'ENEMA'.
(Other definitions for enema that I've seen before include "Bowel evacuator" , "Fluid injected rectally" , "medicine to get you going" , "Medication introduced from behind" , "Colonic irrigation" .)