Best or worst? (8)
I believe the answer is:
overcome
This clue is a double definition.
'best' is the first definition.
(thesaurus)
'worst?' is the second definition.
(worsting is a kind of overcoming)
'or' is the link.
(Other definitions for overcome that I've seen before include "Speechless" , "Succeed in dealing with difficulties" , "Defeat, conquer" , "Beat (an adversary)" , "Master" .)