Some terrifying, unmentionable fellows (6)

I believe the answer is:

gunmen

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'some terrifying unmentionable fellows' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe they are linked in a way I don't understand?

'some terrifying unmentionable fellows' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'GUNMEN' can be found hidden inside 'terrifying unmentionable fellows'.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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