Arch-enemy seems in trouble (7)

I believe the answer is:

nemesis

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

'arch-enemy' is the definition.
I can't judge whether this definition defines the answer.

'seems in trouble' is the wordplay.
'trouble' is an anagram indicator.
'seems'+'in'='seemsin'
'seemsin' anagrammed gives 'NEMESIS'.

Can you help me to learn more?

(Other definitions for nemesis that I've seen before include "Fate" , "Greek god of vengeance" , "Bane" , "rival who can't be beaten" , "Vengeful justice" .)

I've seen this clue in The Mirror.

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