Close to resolving age-old sin (9)
I believe the answer is:
alongside
'close to' is the definition.
(I've seen this before)
'resolving age-old sin' is the wordplay.
'resolving' indicates an anagram.
'age'+'old'+'sin'='ageoldsin'
'ageoldsin' with letters rearranged gives 'ALONGSIDE'.
(Other definitions for alongside that I've seen before include "Parallel to" , "Age-old sin (anag.)" , "Aligned so as to be close to pier" , "Next to, another boat say" , "Bordering" .)