Crossword Genius

Penetrate chapter shunned by middle of America (5)

Ross

I believe the answer is:

enter

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

'penetrate' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for enter that I've seen before include "Fill in" , "Come in - register" , "Fruit drink" , "Come in - penetrate - record" , "Break in" .)

I've seen this clue in The Telegraph.
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