Relative daylight on the Russian plain, say (7)
I believe the answer is:
stepson
'relative' is the definition.
(stepson is a kind of relative)
'daylight on the russian plain say' is the wordplay.
'daylight' becomes 'son' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another.
'the russian plain' becomes 'steppe' (I've seen this in another clue).
'say' indicates a 'sounds like' (homophone) clue.
'steppe' is a homophone of 'step'.
'son' put after 'step' is 'STEPSON'.
Can you help me to learn more?
(Other definitions for stepson that I've seen before include "Child of a spouse by a former marriage" , "No pests about this relation by marriage" , "No pests for male issue of spouse - but not of self" , "Male offspring of partner's former marriage" , "underfoot?" .)