Magic spell beginning to cause damage (5)
I believe the answer is:
charm
'magic spell' is the definition.
(thesaurus)
'beginning to cause damage' is the wordplay.
'beginning to' indicates taking the first letters.
'damage' becomes 'harm' (synonyms).
The initial letter of 'cause' is 'c'.
'c'+'harm'='CHARM'
(Other definitions for charm that I've seen before include "Allure" , "Win over" , "Personal attraction" , "Appeal; trinket" , "pleasing feature" .)