Upset celebrity discounting a rumour (7)
I believe the answer is:
startle
'upset' is the definition.
(thesaurus)
'celebrity discounting a rumour' is the wordplay.
I cannot really understand how this works, but
'celebrity' could be 'star' (I've seen this before) and 'star' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for startle that I've seen before include "Cause shock to" , "Scare" , "Shock, alarm" , "Frighten suddenly" , "Surprise greatly, alarm" .)