Mysterious characters confused nurse (5)
I believe the answer is:
runes
'mysterious characters' is the definition.
(I've seen this in another clue)
'confused nurse' is the wordplay.
'confused' indicates an anagram.
'nurse' anagrammed gives 'RUNES'.
(Other definitions for runes that I've seen before include "Small stones bearing symbols with magic significance" , "old characters" , "marks on old tablets" , "Old letters" , "Mysterious letters" .)