Being by lake provided energy (4)
I believe the answer is:
life
'being' is the definition.
(life is a kind of being)
'by lake provided energy' is the wordplay.
'by' is a charade indicator (letters next to each other).
'lake' becomes 'l'.
'provided' becomes 'if'.
'energy' becomes 'e' (physics symbol as in E=mc2).
'l' put next to 'if' is 'lif'.
'lif'+'e'='LIFE'
(Other definitions for life that I've seen before include "Vitality, vigour" , "Maximum stretch?" , "Existence - biography" , "Actuarial estimate of our remaining years" , "Birth to death" .)