Titan (5)
'titan' is the definition.
(I know that titan can be written as giant)
This is the entire clue.
(Other definitions for giant that I've seen before include "Superhuman being" , "Creature of exceptional size" , "A mighty man like Goliath or Carnera" , "James Dean film (big one!)" , "Large black and white mammal" .)
(Other definitions for czar that I've seen before include "Despot" , "Russian ruler (alt. but not rare spelling)" , "person of great power" , "Russian emperor" , "Pre-1917 Russian ruler" .)