Strange, frightening (5)
I believe the answer is:
eerie
This clue is a double definition.
'strange' is the first definition.
(eerie means odd or strange)
'frightening' is the second definition.
(I've seen this before)
(Other definitions for eerie that I've seen before include "Ghostly" , "Spooky, creepy" , "Uncannily strange" , "Sinister" , "Mysterious" .)