Train Bill to become scintillating (9)
I believe the answer is:
brilliant
'scintillating' is the definition.
(thesaurus)
'train bill to become' is the wordplay.
'to become' indicates an anagram.
'train'+'bill'='trainbill'
'trainbill' is an anagram of 'BRILLIANT'.
(Other definitions for brilliant that I've seen before include "Lustrous" , "Very bright or vivid" , "Shining intensly" , "Very bright or exceptionally talented" , "Bright and sparkling" .)