Carry on to each extreme (9)
I believe the answer is:
persevere
'carry' is the definition.
(thesaurus)
'on to each extreme' is the wordplay.
'on' is a charade indicator (letters next to each other).
'to each' becomes 'per'.
'extreme' becomes 'severe' ('severe' can be a synonym of 'extreme').
'per' next to 'severe' is 'PERSEVERE'.
(Other definitions for persevere that I've seen before include "Persist, stick at" , "Continue despite difficulties" , "Soldier on" , "Hang on in there" , "hold on" .)