Regularly furnished with axes on plain (6)

I believe the answer is:

unsexy

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'plain' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?

'regularly furnished with axes' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'with' is a charade indicator (letters next to each other).
'axes' becomes 'xy' (x axis and y axis).
The alternating letters of 'furnished' are 'unse'.
'unse'+'xy'='UNSEXY'

'on' is the link.

Can you help me to learn more?

(Another definition for unsexy that I've seen is " "not stimulating libido"".)

I've seen this clue in the Sydney Morning Herald.

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