Landmark shows one particular curve (6)

I believe the answer is:

iconic

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'landmark shows one particular curve' is the definition.
I can't tell whether this definition defines the answer.

'one particular curve' is the wordplay.
'one' becomes 'i' (Roman numeral).
'particular curve' becomes 'conic' (I can't explain this - if you can you should give a lot more credence to this answer).
'i'+'conic'='ICONIC'

Can you help me to learn more?

(Other definitions for iconic that I've seen before include "Widely-recognised" , "Worthy of veneration" , "of images" , "Representative or relating to a sacred image" , "admired type" .)

I've seen this clue in The Guardian.

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