Pertaining to an ancient Germanic alphabet (5)
I believe the answer is:
runic
'pertaining to an ancient germanic alphabet' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for runic that I've seen before include "of historic letters" , "Of old magic symbols" , "Pertaining to an ancient Germanic alphabet" , "Like some old characters" , "Like old Scandinavian writing" .)