Concerned with a relation's explanations (7)
I believe the answer is:
reasons
'explanations' is the definition.
(reason is a kind of explanation)
'concerned with a relation's' is the wordplay.
'concerned with' becomes 're'.
'relation' becomes 'sons' (I am not sure about this - if you are sure you should believe this answer much more).
're'+'a'+'sons'='REASONS'
Can you help me to learn more?
(Other definitions for reasons that I've seen before include "Justifications or motives" , "Logically deduces" , "excuses" , "Infers logically" , "Ness oar (anag.)" .)