Knife European left on part of loaf (7)
I believe the answer is:
scalpel
'knife' is the definition.
(scalpel is a kind of knife)
'european left on part of loaf' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'left' becomes 'l' (common abbreviation).
'on' says to put letters next to each other.
'part of loaf' becomes 'scalp' ('loaf' is a slang term for head).
'e'+'l'='el'
'el' put after 'scalp' is 'SCALPEL'.
(Other definitions for scalpel that I've seen before include "Surgeon's tool" , "Surgical tool" , "Small surgical knife" , "Sharp cutting tool" , "One making cuts in hospital" .)