Be unconscious of a slur about honour (7)

I believe the answer is:

slumber

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'be unconscious' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'slur about honour' is the wordplay.
'about' is an insertion indicator.
'honour' becomes 'MBE' (Member of the British Empire award).
'slur' going around 'mbe' is 'SLUMBER'.

'of a' is the link.

Can you help me to learn more?

(Other definitions for slumber that I've seen before include "Drop off" , "nap" , "Snooze" , "snores, maybe?" , "Overnight social event for (American) teenage girls" .)

I've seen this clue in the Evening Standard.

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