With less hair - what nonsense! (10)

I believe the answer is:

balderdash

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'nonsense' is the definition.
(I know that balderdash is a type of nonsense)

'with less hair what' is the wordplay.
'with less hair' becomes 'balder' (I've seen this before).
'what' becomes 'dash' (I can't explain this - if you can you should give a lot more credence to this answer).
'balder'+'dash'='BALDERDASH'

Can you help me to learn more?

(Other definitions for balderdash that I've seen before include "tripe" , "Poppycock" , "garbage" , "rot" , "bull" .)

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

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