a military unit consisting of foreign volunteers in the service of a state.
2.
(initial capital letters) a specialized military unit of the French army, consisting of volunteers of all nationalities assigned to military operations and duties outside France.
Origin
1880-85, Americanism
Examples from the web for foreign legion
They have now joined a burgeoning foreign legion in the world's richest, and perhaps best league.
British Dictionary definitions for foreign legion
foreign legion
noun
1.
a body of foreign volunteers serving in an army, esp that of France