Unsettling fellow about to peer back (5)

I believe the answer is:

creep

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'unsettling fellow' is the definition.
I can't judge whether this defines the answer.

'about to peer back' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to' means one lot of letters go next to another.
'back' is a reversal indicator.
'peer' back-to-front is 'reep'.
'c'+'reep'='CREEP'

Can you help me to learn more?

(Other definitions for creep that I've seen before include "Crawl; skulk" , "Move with stealth" , "Slink" , "Obsequious person" , "jerk?" .)

I've seen this clue in The Mirror.

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