Suppose plenipotentiary's to some extent revolutionary (5)
I believe the answer is:
opine
'suppose' is the definition.
(I've seen this in another clue)
'plenipotentiary's to some extent revolutionary' is the wordplay.
'to some extent' indicates a hidden word.
'revolutionary' is a reversal indicator (letters revolve around).
'enipo' can be found hidden inside 'plenipotentiarys'.
'enipo' in reverse letter order is 'OPINE'.
(Other definitions for opine that I've seen before include "Think - express a view" , "Give opinion" , "Suppose" , "Proffer a view" , "Suggest" .)