Monstrous, false friend binned flares (5)

I believe the answer is:

fiend

I'm a little stuck... Click here to teach me more about this clue!

'monstrous false friend' is the definition.
'fiend' can be an answer for 'friend' (fiend is a kind of friend). I am unsure of the 'monstrous false' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for fiend that I've seen before include "Demon; cruel person" , "Evil supernatural being" , "Devil" , "addict" , "Operatic super-soprano" .)

I've seen this clue in The Irish Times.

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