Tyrannical cops tied up (8)
I believe the answer is:
despotic
'tyrannical' is the definition.
('despotic' can be a synonym of 'tyrannical')
'cops tied up' is the wordplay.
'up' indicates an anagram.
'cops'+'tied'='copstied'
'copstied' is an anagram of 'DESPOTIC'.
(Other definitions for despotic that I've seen before include "Ruling harshly" , "High-handed" , "Dictatorial" , "'Cruel and oppressive, as a dictator (8)'" , "Exercising absolute power" .)