Unintentional (10)
'unintentional' is the definition.
(synonyms)
This is all the clue.
(Other definitions for accidental that I've seen before include "Sign raising or lowering a musical note" , "Possible sharp" , "Subsidiary" , "indication to modify tone slightly" , "without planning" .)
'unintentional' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for inadvertent that I've seen before include "without meaning" , "Careless" , "Unintentional" , "unguarded" , "Unthinking" .)