Oppressive individual, awake endlessly (7)

I believe the answer is:

onerous

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'oppressive' is the definition.
(onerous can mean crushing or oppressive)

'individual awake endlessly' is the wordplay.
'individual' becomes 'one' (an individual is one person).
'awake endlessly' becomes 'rous' (I can't justify this - if you can you should believe this answer much more).
'one'+'rous'='ONEROUS'

Can you help me to learn more?

(Other definitions for onerous that I've seen before include "Burdensome, heavy kind of duty" , "Effortful" , "Trying" , "Difficult, troublesome" , "Challenging" .)

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