Month of a Roman emperor (6)
I believe the answer is:
august
'month of a roman emperor' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for august that I've seen before include "which is supposedly hot" , "Month named after emperor of Rome" , "Dignified - time of year" , "Roman emperor's month" , "For Edna O'Brien, it was a 27 across month" .)