European nerd has removed top (5)
I believe the answer is:
greek
'european' is the definition.
(I know that Greek is a type of european)
'nerd has removed top' is the wordplay.
'nerd' becomes 'geek' (I've seen this before).
'has' means one lot of letters goes inside another.
'top' says to take the initial letters.
The initial letter of 'removed' is 'r'.
'geek' enclosing 'r' is 'GREEK'.
(Other definitions for greek that I've seen before include "Hellene" , "From Thessaloniki, perhaps" , "Foreigner" , "One from Salonika" , "Nationality" .)