Scandinavian river feature outside (5)
I believe the answer is:
norse
'scandinavian' is the definition.
(Norse can mean relating to ancient Scandinavia)
'river feature outside' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'feature' becomes 'nose' (I've seen this before).
'outside' indicates putting letters inside.
'r' going within 'nose' is 'NORSE'.
(Other definitions for norse that I've seen before include "Language - senor! (anag)" , "Old Scandinavian language" , "Northern European" , "Relating to ancient Scandinavian" , "like the Valkyries?" .)