Brother maybe supporting sister, receiving love for that? (8,7)
I believe the answer is:
relative pronoun
'for that?' is the definition.
I can't judge whether this definition defines the answer.
'brother maybe supporting sister receiving love' is the wordplay.
'brother maybe' becomes 'relative' (I am not sure about this - if you are sure you should believe this answer much more).
'supporting' becomes 'pro' (being pro something is supporting it).
'sister' becomes 'nun' (nuns are referred to as sister).
'receiving' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'nun' enclosing 'o' is 'noun'.
'relative'+'pro'+'noun'='RELATIVE PRONOUN'
Can you help me to learn more?
(Other definitions for relative pronoun that I've seen before include "Say which" , "It could be that" , "Maybe what" .)