Sinister country Spain on reflection (5)
I believe the answer is:
eerie
'sinister' is the definition.
(I've seen this before)
'country spain on reflection' is the wordplay.
'country' becomes 'eire' (Eire is an example).
'spain' becomes 'e' (abbreviation for Espana).
'on reflection' shows that the letters should be reversed in order.
'eire'+'e'='eiree'
'eiree' backwards is 'EERIE'.
(Other definitions for eerie that I've seen before include "Spine-tingling" , "Spooky, supernatural" , "Scary, weird" , "Spooky, weird" , "Strangely frightening" .)