Dull song Queen once released (4)

I believe the answer is:

numb

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'dull' is the definition.
(I know that dull can be written as numb)

I don't understand the remainder of the clue.

(Other definitions for numb that I've seen before include "Feeling nothing" , "Unable to feel or think" , "Deadened, desensitised" , "Unable to move" , "Anaesthetised, unfeeling" .)

I've seen this clue in The Independent.

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