Crossword Genius

Support playwright retaining current share (10)

Ross

I believe the answer is:

proportion

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'support playwright' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'retaining current share' is the wordplay.
'retaining current' becomes 'pro' (I can't justify this - if you can you should give a lot more credence to this answer).
'share' becomes 'portion' ('portion' can be a synonym of 'share').
'pro'+'portion'='PROPORTION'

Can you help me to learn more?

(Other definitions for proportion that I've seen before include "balance" , "Part - one needs a sense of it" .)

I've seen this clue in The Independent.
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