Called one in, penitent (5)
I believe the answer is:
ruing
'penitent' is the definition.
The definition and answer are not the same part of speech.
'called one in' is the wordplay.
'called' becomes 'rung' (ring can mean to call on the phone).
'one' becomes 'I' (Roman numeral).
'in' is an insertion indicator.
'rung' going around 'i' is 'RUING'.
Can you help me to learn more?
(Other definitions for ruing that I've seen before include "Feeling sorry for" , "Having second thoughts" , "Bitterly regretting" , "full of remorse?" , "Feeling bad" .)