Rebuke son without emotion (5)
I believe the answer is:
scold
'rebuke' is the definition.
(I know that rebuke can be written as scold)
'son without emotion' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'without emotion' becomes 'cold'.
's'+'cold'='SCOLD'
(Other definitions for scold that I've seen before include "Upbraid" , "Castigate" , "Censure, berate" , "Rate" , "Chide - nag" .)