Not as much energy expended at first for tenant (6)
I believe the answer is:
'tenant' is the definition.
(I know that tenant can be written as lessee)
'not as much energy expended at first' is the wordplay.
'not as much' becomes 'less' (similar in meaning).
'at first' suggests taking the first letters.
The initial letters of 'energy expended' is 'ee'.
'for' acts as a link.
(Other definitions for lessee that I've seen before include "One renting a property", "Who pays the rent", "Contractor", "One holding lease on property", "Tenant who holds a lease".)