D for dimwit? (10)

I believe the answer is:

dunderhead

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This clue might be a double definition.

'd for' is the first definition.
The definition suggests a singular noun which matches the answer.

'dimwit?' is the second definition.
(I know that blockhead can be written as dunderhead)

Can you help me to learn more?

(Other definitions for dunderhead that I've seen before include "fool" , "dumbass?" , "Dunce" , "Ignoramus" , "Idiot" .)

I've seen this clue in The Times.

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