The first Tsar? I haven't a clue (4,3,8)
I believe the answer is:
ivan the terrible
'a clue' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'the first tsar? i haven't' is the wordplay.
'first' is a charade indicator (letters next to each other).
'tsar?' becomes 'Ivan' (name of several Russian tsars).
'i haven't' becomes 'terrible' (I can't explain this - if you can you should believe this answer much more).
'the' put after 'ivan' is 'ivanthe'.
'ivanthe'+'terrible'='IVAN THE TERRIBLE'
Can you help me to learn more?
(Other definitions for ivan the terrible that I've seen before include "Old ruler" , "Russian leader's" , "Russian leader" , "despot" , "Cruel tyrant" .)