Has boil, festering, to get rid of (7)
I believe the answer is:
abolish
'get rid of' is the definition.
('abolish' can be a synonym of 'get rid of')
'has boil festering' is the wordplay.
'festering' indicates an anagram.
'has'+'boil'='hasboil'
'hasboil' is an anagram of 'ABOLISH'.
'to' is the link.
(Other definitions for abolish that I've seen before include "Nullify" , "Put an end to, a rule perhaps" , "ditch" , "Scrap" , "Do away with, rescind" .)