Agreed plan working on new vaccine (10)

I believe the answer is:

connivance

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'agreed plan' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'working on new vaccine' is the wordplay.
'working' is an anagram indicator.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'on'+'n'+'vaccine'='onnvaccine'
'onnvaccine' with letters rearranged gives 'CONNIVANCE'.

Can you help me to learn more?

(Other definitions for connivance that I've seen before include "Passive co-operation" , "Act of conspiracy" , "working in cahoots" .)

I've seen this clue in The Independent.

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