Catholic Pole in awful choir is persistent in a sick way (7)

I believe the answer is:

chronic

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'persistent in a sick way' is the definition.
I can't tell whether this definition defines the answer.

'catholic pole in awful choir' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'pole' becomes 'n'.
'in' indicates putting letters inside.
'awful' is an anagram indicator.
'choir' anagrammed gives 'hroic'.
'n' placed into 'hroic' is 'hronic'.
'c'+'hronic'='CHRONIC'

'is' acts as a link.

Can you help me to learn more?

(Other definitions for chronic that I've seen before include "pants" , "Long-continuing" , "(Of an illness) persistent" , "(Of illness) lengthy; very bad (colloq.)" , "(Of a problem) long-lasting" .)

I've seen this clue in the Irish Times.

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