Inaction of holy person, a nun half forgotten (6)
I believe the answer is:
stasis
'inaction' is the definition.
(I know that stasis is a type of inaction)
'holy person a nun half forgotten' is the wordplay.
'holy person' becomes 'st' (short for saint).
'nun' becomes 'sister' (a nun might be called sister).
'half forgotten' indicates taking half.
'sister' with half the letters taken is 'sis'.
'st'+'a'+'sis'='STASIS'
'of' acts as a link.
(Other definitions for stasis that I've seen before include "Stoppage, arrest" , "Secret police force's" , "No progressive state" , "Enduring state" , "Cessation" .)