Extremely effete raider oddly unsettling (5)
I believe the answer is:
eerie
'unsettling' is the definition.
(I've seen this in another clue)
'extremely effete raider oddly' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'oddly' indicates alternate letters (letters in odd-numbered positions).
'effete' with its middle removed is 'ee'.
The alternating letters of 'raider' are 'rie'.
'ee'+'rie'='EERIE'
(Other definitions for eerie that I've seen before include "Scary, weird" , "Spooky, supernatural" , "Strange and disturbing" , "Spooky, macabre" , "Awesome" .)