Heavy individual to awaken without energy (7)
I believe the answer is:
onerous
'heavy' is the definition.
('onerous' can be similar in meaning to 'heavy')
'individual to awaken without energy' is the wordplay.
'individual' becomes 'one' (**).
'to awaken' becomes 'rouse' (I've seen this before).
'without' suggests deleting specific letters.
'energy' becomes 'e' (physics symbol as in E=mcn).
'rouse' with 'e' taken out is 'rous'.
'one'+'rous'='ONEROUS'
(Other definitions for onerous that I've seen before include "Challenging" , "Burdensome as duty may be" , "Involving a great deal of effort" , "Heavy, difficult to do or bear" , "Burdensome, taxing" .)