It's not this that's emphatic! (4)
I believe the answer is:
half
'it's not this that's emphatic' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for half that I've seen before include "Two of which make the whole" , "alcoholic drink" , "Measure of beer" , "shared round" , "50 per cent" .)