Complaint about a gumboil one ignored (7)
I believe the answer is:
lumbago
'complaint' is the definition.
(I've seen this before)
'about a gumboil one ignored' is the wordplay.
'about' indicates an anagram.
'one' becomes 'i' (Roman numeral).
'ignored' suggests deleting specific letters.
'gumboil' with 'i' taken out is 'gumbol'.
'a'+'gumbol'='agumbol'
'agumbol' anagrammed gives 'LUMBAGO'.
(Other definitions for lumbago that I've seen before include "Rheumatic backache" , "Rheumatic pain in muscles of lower back" , "Back problem" , "Lower back ache" , "Maul bog badly for a rheumatic affliction" .)