Shakespearean clown flushed and was rotten (8)

I believe the answer is:

festered

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'rotten' is the definition.
The answer and definition are different parts of speech. However, adjectives and past participle verbs sometimes define each other.

'shakespearean clown flushed' is the wordplay.
'shakespearean clown' becomes 'feste' (I've seen this in another clue).
'flushed' becomes 'red' (red-faced).
'feste'+'red'='FESTERED'

'and was' is the link.

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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