European nurse possibly wanting guarantee (6)
I believe the answer is:
ensure
'guarantee' is the definition.
(I know that guarantee can be written as ensure)
'european nurse possibly' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'possibly' is an anagram indicator.
'nurse' anagrammed gives 'nsure'.
'e'+'nsure'='ENSURE'
'wanting' is the link.
(Other definitions for ensure that I've seen before include "Make certain for the future" , "Make certain (something will occur)" , "warrant" , "Make certain, confirm" , "Make certain or safe" .)