Autocratic detectives return about poet's composition (8)
I believe the answer is:
despotic
'autocratic' is the definition.
(I know that autocratic can be written as despotic)
'detectives return about poet's composition' is the wordplay.
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'return' says the letters should be written backwards.
'about' means one lot of letters goes inside another.
'composition' indicates anagramming the letters.
'cid' backwards is 'dic'.
'poets' anagrammed gives 'espot'.
'dic' going around 'espot' is 'DESPOTIC'.
(Other definitions for despotic that I've seen before include "Authoritarian" , "of tyrant" , "Like a cruel ruler" , "Cruelly oppressive" , "Autocratic" .)