So loveless and pure, perhaps, but brilliant (5)
I believe the answer is:
super
'brilliant' is the definition.
(I've seen this before)
'so loveless and pure perhaps' is the wordplay.
'so loveless' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'and' means one lot of letters go next to another.
'perhaps' indicates an anagram.
'pure' with letters rearranged gives 'uper'.
's'+'uper'='SUPER'
'but' acts as a link.
Can you help me to learn more?
(Other definitions for super that I've seen before include "Topnotch, terrific" , "Excellent; police officer" , "of high quality" , "Delightful" , "Gushily great, excellent" .)