Displeasure at duke’s insecurity (6)
I believe the answer is:
danger
'insecurity' is the definition.
(I've seen this before)
'displeasure at duke's' is the wordplay.
'displeasure' becomes 'anger' (I've seen this in another clue).
'at' says to put letters next to each other (I've seen this in other clues).
'duke' becomes 'd' (abbreviation).
'anger' after 'd' is 'DANGER'.
(Other definitions for danger that I've seen before include "Ranged about in some peril" , "Garden (anag) - peril" , "Red flag, for example" , "Insecurity" , "Peril, exposure to harm" .)