Secure northern European cosmetic treatment (4,6)
I believe the answer is:
nail polish
'cosmetic treatment' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'secure northern european' is the wordplay.
'secure' becomes 'nail' (both can mean to apprehend or capture).
'northern european' becomes 'polish' (Poland is in Europe. I am not sure about the 'northern' bit.).
'nail'+'polish'='NAIL-POLISH'
Can you help me to learn more?
(Other definitions for nail polish that I've seen before include "digital coverage" , "cosmetic" , "digital application" .)