Manage in charge of old Scandinavian? (5)
I believe the answer is:
runic
'of old scandinavian?' is the definition.
(old Scandinavian was written with runes)
'manage in charge' is the wordplay.
'manage' becomes 'run' (both can mean to organise).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'run'+'ic'='RUNIC'
(Other definitions for runic that I've seen before include "Like mysterious characters" , "character hard to interpret" , "Using Norse letters" , "Relating to an ancient Scandinavian alphabet" , "Of old magic symbols" .)