Alarm worried Rupert Bear, initially (7)
I believe the answer is:
perturb
'alarm' is the definition.
(thesaurus)
'worried rupert bear initially' is the wordplay.
'worried' indicates anagramming the letters.
'initially' says to take the initial letters.
The first letter of 'bear' is 'b'.
'rupert' is an anagram of 'pertur'.
'pertur'+'b'='PERTURB'
(Other definitions for perturb that I've seen before include "Discountenance" , "Disturb - trouble" , "upset" , "Disquiet, disturb" , "Make uneasy or cause to be worried" .)