One’s predecessor reacts on being corrected (8)
I believe the answer is:
ancestor
'one's predecessor' is the definition.
(an ancestor who came before someone)
'reacts on being corrected' is the wordplay.
'being corrected' indicates an anagram.
'reacts'+'on'='reactson'
'reactson' is an anagram of 'ANCESTOR'.
(Other definitions for ancestor that I've seen before include "An escort (anag.)" , "not being of the modern generation" , "descent comes from one" , "Forefather" , "Adam was our first one" .)