Reluctant and regretting going topless, full of new resolve (9)
I believe the answer is:
unwilling
'reluctant' is the definition.
(similar in meaning)
'regretting going topless full of new resolve' is the wordplay.
'regretting' becomes 'ruing' ('rue' can be a synonym of 'regret').
'going topless' means to remove the first letter.
'full of' indicates putting letters inside.
'new' becomes 'n'.
'resolve' becomes 'will' (I've seen this before).
'ruing' with its initial letter taken away is 'uing'.
'n'+'will'='nwill'
'uing' placed around 'nwill' is 'UNWILLING'.
'and' acts as a link.
(Other definitions for unwilling that I've seen before include "Loth" , "Reluctant" , "Disinclined" , "resistant?" , "Those leaving nothing, legally so" .)