Warhorse, no stallion, with new energy (7)
I believe the answer is:
marengo
'warhorse' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'no stallion with new energy' is the wordplay.
'no stallion' becomes 'mare' (I am not sure about this - if you are sure you should believe this answer much more).
'with' says to put letters next to each other.
'new' becomes 'n' (abbreviation as in New Testament NT).
'energy' becomes 'go' (go can mean energy or enthusiasm).
'mare'+'n'+'go'='MARENGO'
Can you help me to learn more?
(Other definitions for marengo that I've seen before include "Napoleonic victory in 1800" , "vegetables and wine" , "Battle of the Napoleonic Wars in Piedmont" , "Victory for Napoleon in Italy" , "Napoleon's horse" .)