Entails becoming outstanding (7)
I believe the answer is:
salient
'outstanding' is the definition.
(I know that outstanding can be written as salient)
'entails becoming' is the wordplay.
'becoming' indicates an anagram.
'entails' with letters rearranged gives 'SALIENT'.
(Other definitions for salient that I've seen before include "part of defences" , "Prominent - in tales (anag)" , "Prominent, most noticeable" , "Outstanding - it's lean (anag)" , "Noteworthy" .)