Understand Roman emperor’s limits in Hell (7)
I believe the answer is:
inferno
'hell' is the definition.
(synonyms)
'understand roman emperor's limits' is the wordplay.
'understand' becomes 'infer' (synonyms).
'roman emperor' becomes 'nero' (I've seen this before).
'limits' means to remove the middle letters.
'nero' with its centre taken out is 'no'.
'infer'+'no'='INFERNO'
'in' acts as a link.
(Other definitions for inferno that I've seen before include "Nine Circles here" , "blazer?" , "Uncontrollable fire" , "Hellish poem" , "Fierce fire" .)