Answer about thickness (5)

I believe the answer is:

'answer' is the definition.
(I know that answer can be written as reply)

'about thickness' is the wordplay.
'about' becomes 're' (regarding).
'thickness' becomes 'ply' (I have seen 'Thickness of yarn ' mean 'ply' so perhaps 'thickness' could also mean 'ply').
're'+'ply'='REPLY'

(Other definitions for reply that I've seen before include "Come back" , "Reciprocate" , "acknowledgement" , "Return" , "response is demanded" .)

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

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