Publicly expose a lightweight understudy (8)
I believe the answer is:
'understudy' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how one could define the other.
'publicly expose a lightweight' is the wordplay.
'publicly expose' becomes 'den' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a lightweight' becomes 'ounce' (I've seen this before).
Can you help me to learn more?
(Other definitions for denounce that I've seen before include "Speak violently against" , "Revile" , "As threat, identify" , "Speak publicly against, censure" , "Inform against (someone)" .)