One robbery involves tyrant (4)
I believe the answer is:
nero
'tyrant' is the definition.
(Nero was a Roman tyrant)
'one robbery involves' is the wordplay.
'involves' says the answer is hidden in the clue.
'NERO' can be found hidden inside 'one robbery'.
(Other definitions for nero that I've seen before include "Emperor, 'burnt' Rome" , "Emperor (who fiddled while Rome burned?) d. AD68" , "Roman emperor who fiddled while Rome burned" , "Tyrannical Roman emperor" , "Barbarous Roman emperor" .)