Ancient letter or mystical symbol (4)
I believe the answer is:
rune
I believe this is a double definition.
'ancient letter' is the first definition.
(I've seen this in another clue)
'mystical symbol' is the second definition.
(I've seen this before)
(Other definitions for rune that I've seen before include "Letter of an ancient Germanic alphabet" , "Mystic symbol" , "Old alphabet letter" , "Old Scandinavian letter" , "Ancient symbol" .)