Not the final temperature (4)
I believe the answer is:
heat
'temperature' is the definition.
(I know that heat is a type of temperature)
'not the final' is the wordplay.
'not' becomes 'hea' (I can't justify this - if you can you should give a lot more credence to this answer).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'final' says to put letters next to each other.
'hea'+'t'='HEAT'
Can you help me to learn more?
(Other definitions for heat that I've seen before include "High temperature" , "It's measured in therms" , "Warm up" , "Energy that caues a rise in temperature" , "Energy that causes a rise in temperature" .)