Diabolical
'diabolical' is the definition.
(I know that diabolical can be written as fiendish)
This is all the clue.
(Other definitions for fiendish that I've seen before include "Finished (anag) - demonic" , "This Sudoku" , "like some Sudokus" , "Extremely cruel" , "Diabolic" .)
(Other definitions for satanic that I've seen before include "Relating to the devil" , "Devilish, like Blake's mills" , "Bad" , "Fiendish" , "Devilish (as Blake's 18)" .)
'diabolical' is the definition.
(I know that diabolical can be written as demonic)
This is the entire clue.
(Other definitions for demonic that I've seen before include "Wicked" , "Cruel like the devil" , "diabolical" , "Resembling evil spirits" , "Devilish" .)
'diabolical' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for evil that I've seen before include "Malign" , "Extremely bad" , "very naughty" , "Great wickedness" , "A live sort of badness" .)