The tongue of a World War One field marshal (6)
I believe the answer is:
french
I believe this clue is a double definition.
'the tongue' is the first definition.
(French is an example)
'a world war one field marshal' is the second definition.
(John French, 1st Earl of Ypres)
'of' is the link.
(Other definitions for french that I've seen before include "Shellac dissolved in alcohol, used on furniture" , "- Cricket; - dressing" , "Word which may precede bean, chalk, cricket, horn" , "Gallic" , "A Romance language" .)