Australia (the country) is completely surrounded by water, so it is an island. Australia, according to google..com, Australia is an island and a country.
Australia is a continent. Both Americas are also surrounded by sea and oceans... So those are also island? And yeah Africa and Euro-Asia are also surrounded by ocean waters.. so is Antarctica.
The Caspian Sea is the world's largest lake and is more than 4x bigger in area than Lake Superior, which is the world's largest freshwater lake. Maybe consider adding that as a qualification?
Area of Greenland: 836,300 sq miles (2.166 million km²)---------------------------
No one should be saying Greenland is a larger island than Australia. Look at the facts!