European king wearing anorak (5)
I believe the answer is:
greek
'european' is the definition.
(I know that Greek is a type of european)
'king wearing anorak' is the wordplay.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'wearing' is an insertion indicator.
'anorak' becomes 'geek' (both can mean a nerdy person).
'r' placed into 'geek' is 'GREEK'.
(Other definitions for greek that I've seen before include "Mediterranean native" , "Person from Athens" , "Language proverbially unknown to one" , "Classical language" , "From Thessaloniki, perhaps" .)