Simple geograpical feature (5)

I believe the answer is:

plain

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'feature' is the definition.
(I have seen 'Geographical feature' mean 'plain' so perhaps 'feature' could also mean 'plain')

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for plain that I've seen before include "Unprepossessing" , "stretch of level land" , "Unadorned on flat area" , "Unflavoured" , "lacking special beauty" .)

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