1.
Greater is the comparative of great .
2.
Greater is used with the name of a large city to refer to the city together with the surrounding urban and suburban area.
...Greater London.
ADJ: ADJ n
3.
Greater is used with the name of a country to refer to a larger area which includes that country and other land which used to belong to it, or which some people believe should belong to it.
...~ Syria.
ADJ: ADJ n