Amazing jump by Heather (9)
I believe the answer is:
startling
'amazing' is the definition.
(thesaurus)
'jump by heather' is the wordplay.
'jump' becomes 'start' ('start' can be a synonym of 'jump'**).
'by' means one lot of letters go next to another.
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
'start'+'ling'='STARTLING'
(Other definitions for startling that I've seen before include "Surprising or alarming" , "Jaw-dropping" , "Rattlings of alarming kind" , "Producing sudden alarm" , "Surprising, shocking" .)