Thus, again, is painful (4)

I believe the answer is:

sore

'painful' is the definition.
(synonyms)

'thus again' is the wordplay.
'thus' becomes 'so' (synonyms).
'again' becomes 're'.
'so'+'re'='SORE'

'is' is the link.

(Other definitions for sore that I've seen before include "Painful spot" , "Aching; severe" , "Painful, or the source of pain" , "Hurting, painful" , "source of distress" .)

I've seen this clue in the Evening Standard.

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