Cure from extreme dysentery (6)
I believe the answer is:
remedy
'cure' is the definition.
(synonyms)
'from extreme dysentery' is the wordplay.
'from' says the answer is hidden in the clue.
'REMEDY' is hidden within 'extreme dysentery'.
(Other definitions for remedy that I've seen before include "Medicine or therapy that cures disease or relieves pain" , "Cure for illness" , "Curative medicine" , "Cure for disease or difficulty" , "Medication" .)