Essentially deem ancient times a misery! (6)
I believe the answer is:
eeyore
'a misery' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'essentially deem ancient times' is the wordplay.
'essentially' means to look at the middle letters.
'ancient times' becomes 'yore' (I've seen this in another clue).
The central letters of 'deem' are 'ee'.
'ee'+'yore'='EEYORE'
Can you help me to learn more?
(Other definitions for eeyore that I've seen before include "One of Pooh's friends" , "miserable ass" , "Despondent figure" , "Pooh's gloomy donkey friend" , "Fictional donkey" .)