Awful description of first Russian tsar (8)
I believe the answer is:
'awful' is the definition.
(I know that awful can be written as terrible)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for terrible that I've seen before include "Frightful" , "Appalling" , "Extremely bad" , "Atrocious" , "Really bad" .)