The King hid letters in a roguish manner (8)
I believe the answer is:
devilish
'hid letters in a roguish manner' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs can occasionally mean the same thing.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for devilish that I've seen before include "like Screwtape" , "Very difficult to deal with" , "Very wicked" , "naughty" , "Diabolical" .)