Frenchman appears in some French battlefield (5)
I believe the answer is:
somme
'french battlefield' is the definition.
'somme' can be an answer for 'battlefield' (I've seen this before). I am not sure about the 'french' bit.
'frenchman appears in some' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'appears in' means one lot of letters goes inside another.
'm' placed into 'some' is 'SOMME'.
Can you help me to learn more?
(Other definitions for somme that I've seen before include "French river known from World War 1" , "French river known from First World War" , "Scene of World War One battles" , "World War I battlefield around French river" , "French river, scene of 1916 battles" .)