Blunder or incident is unsettling (12)
I believe the answer is:
indiscretion
'blunder' is the definition.
(thesaurus)
'or incident is unsettling' is the wordplay.
'unsettling' indicates anagramming the letters.
'or'+'incident'+'is'='orincidentis'
'orincidentis' with letters rearranged gives 'INDISCRETION'.
(Other definitions for indiscretion that I've seen before include "Imprudence" , "Slip" , "Tactless deed" , "Rashness" , "Tactless remark or action" .)