Sinister member of the nobility over in Cyprus (6)
I believe the answer is:
creepy
'sinister' is the definition.
(I've seen this before)
'member of the nobility over in cyprus' is the wordplay.
'member of the nobility' becomes 'peer' (I've seen this before).
'over' says the letters should be written backwards.
'in' is an insertion indicator.
'cyprus' becomes 'cy' (abbreviation).
'peer' backwards is 'reep'.
'reep' put within 'cy' is 'CREEPY'.
(Other definitions for creepy that I've seen before include "Likely to cause goose pimples" , "Causing feelings of fear or repulsion" , "Disturbing, crawly" , "Threatening" , "Annoying and unpleasant" .)