Flat B from the rear? (5)

I believe the answer is:

banal

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

'b from the rear?' is the wordplay.
'from the rear?' becomes 'anal' (I am not sure about this - if you are sure you should believe this answer much more).
'b'+'anal'='BANAL'

Can you help me to learn more?

(Other definitions for banal that I've seen before include "Obvious and dull" , "boringly dull" , "Overfamiliar through overuse" , "lacking interest?" , "'Trite, time-worn (5)'" .)

I've seen this clue in The Independent.

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