A bitterly free rendering (2,7)

I believe the answer is:

at liberty

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'rendering' is the definition.
The definition and answer are not the same part of speech.

'a bitterly free' is the wordplay.
'free' is an anagram indicator.
'bitterly' anagrammed gives 'tliberty'.
'a'+'tliberty'='AT LIBERTY'

Can you help me to learn more?

(Other definitions for at liberty that I've seen before include "Free, not confined" , "Available" , "Not imprisoned" .)

I've seen this clue in The Irish Independent.

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