Not a soul has energy after midday (2-3)
I believe the answer is:
no one
'not a soul' is the definition.
(I've seen this before)
'energy after midday' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'after' says to put letters next to each other.
'midday' becomes 'noon' (synonyms).
'e' after 'noon' is 'NO-ONE'.
'has' acts as a link.
(Other definitions for no one that I've seen before include "Not a single person" , "Not a soul" , "Cipher" , "Nobody" , "Failure" .)