Army group (4)
'army group' is the definition.
(group of soldiers)
This is the entire clue.
(Other definitions for unit that I've seen before include "Military team" , "Item combining separate parts" , "Subdivision of a whole" , "Individual thing; one" , "Self-contained part" .)
'army group' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for legion that I've seen before include "Large military force" , "Roman battalion" , "A great number in the Roman military unit" , "Division of ancient Roman army" , "Military force - in Lego (anag)" .)