Prove false prisoner passed judgement (8)
I believe the answer is:
confound
'prove false' is the definition.
The answer and definition can be both related to thinking as well as being verbs in their base form.
Maybe you can see a link between them that I can't see?
'prisoner passed judgement' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'passed judgement' becomes 'found' (I can't justify this - if you can you should give a lot more credence to this answer).
'con'+'found'='CONFOUND'
Can you help me to learn more?
(Other definitions for confound that I've seen before include "Surprise, confuse" , "Nonplus" , "Thwart - baffle" , "Prove wrong; confuse" , "Bewilder" .)