Crossword Genius

Companion eliminating king's bad guy (5)

Ross

I believe the answer is:

fiend

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'bad guy' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for fiend that I've seen before include "Devilish person" , "Evil spirit, demon" , "monster" , "addict" , "Wicked and inhuman person" .)

I've seen this clue in The Independent.
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