Experience is less than energy (7)
I believe the answer is:
undergo
'experience' is the definition.
(synonyms)
'less than energy' is the wordplay.
'less than' becomes 'under' (eg under a certain number).
'energy' becomes 'go' (I've seen this in other clues).
'under'+'go'='UNDERGO'
'is' is the link.
(Other definitions for undergo that I've seen before include "Endure for guerdon" , "Experience, be subjected to" , "Guerdon (anag.)" , "Endure, experience something" , "Experience or live through" .)