Not willing to be ill (10)

I believe the answer is:

indisposed

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'be ill' is the definition.
('indisposed' can be similar in meaning to 'ill')

'not willing' is the wordplay.
'not' becomes 'in' (I can't justify this - if you can you should give a lot more credence to this answer).
'willing' becomes 'disposed' ('disposed' can be similar in meaning to 'willing').
'in'+'disposed'='INDISPOSED'

'to' is the link.

Can you help me to learn more?

(Other definitions for indisposed that I've seen before include "Slightly unwell" , "Poorly" , "Out of sorts" .)

I've seen this clue in The Telegraph.

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