Anything that can reform a thug (5)
I believe the answer is:
aught
'anything that' is the definition.
'aught' can be an answer for 'anything' ('aught' means anything). I am not sure about the remainder of the definition.
'reform a thug' is the wordplay.
'reform' is an anagram indicator (letters in a new form).
'a'+'thug'='athug'
'athug' with letters rearranged gives 'AUGHT'.
'can' acts as a link.
Can you help me to learn more?
(Other definitions for aught that I've seen before include "Anything (Shakespearean)" , "Anything at all (archaic)" , "Nothing" , "Emphatically anything" .)