Soldier eats a blue biscuit (9)
I believe the answer is:
garibaldi
'biscuit' is the definition.
(I've seen this before)
'soldier eats a blue' is the wordplay.
'soldier' becomes 'GI' (GI can mean a US soldier).
'eats' means one lot of letters goes inside another.
'blue' becomes 'ribald' (synonyms).
'a'+'ribald'='aribald'
'gi' placed around 'aribald' is 'GARIBALDI'.
(Other definitions for garibaldi that I've seen before include "Blouse; biscuit; Italian patriot" , "Lady's blouse" , "Italian leader; biscuit" , "Revolutionary leader" , "21 across hero" .)