Young relative — one that shines, we hear (3)
I believe the answer is:
son
'young relative' is the definition.
(a child)
'one that shines we hear' is the wordplay.
'one that shines' becomes 'sun' (the sun shines).
'we hear' shows a homophone (sound like).
'sun' sounds like 'SON'.
(Other definitions for son that I've seen before include "Male descendant" , "Male scion" , "Native" , "Human offspring" , "The kind of child" .)