Firm around middle (4)

I believe the answer is:

core

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

'middle' is the definition.
(core can mean the centre of something)

'firm around' is the wordplay.
'firm' becomes 'co' (abbreviation for company).
'around' becomes 're' (I can't justify this - if you can you should believe this answer much more).
'co'+'re'='CORE'

Can you help me to learn more?

(Other definitions for core that I've seen before include "Crux" , "Inner part" , "Central zone" , "Drilled rock sample" , "Planet's centre" .)

I've seen this clue in The Mirror.

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