Crossword Genius

Source of thickness of Cockney school base? (9)

Ross

I believe the answer is:

arrowroot

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'source of thickness of cockney school base?' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'cockney school base?' is the wordplay.
'cockney school' becomes ''arrow' ('Harrow' - famous UK public school - said with the 'H' dropped - a cockney accent.).
'base?' becomes 'root' (synonyms).
'arrow'+'root'='ARROWROOT'

Can you help me to learn more?

(Other definitions for arrowroot that I've seen before include "culinary powder" , "Medicinal plant" , "Starchy plant" , "Fine cooking powder" , "that thickens" .)

I've seen this clue in The Telegraph.
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