Rate son lacking in emotion (5)
I believe the answer is:
scold
'rate' is the definition.
(I've seen this before)
'son lacking in emotion' is the wordplay.
I cannot really see how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found within the answer.
The remaining letters 'cold' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for scold that I've seen before include "Chide - nag" , "Complaining woman" , "Upbraid" , "Rate" , "Chide - fishwife" .)