Big gun and Luminary

Big gun noun - One of high position or importance within a group.

Luminary and big gun are semantically related. in dignitary topic. In some cases you can use "Luminary" instead a noun phrase "Big gun", when it comes to topics like high ranking person.

Luminary noun - A ball-shaped gaseous celestial body that shines by its own light.

Big gun and luminary are semantically related. Sometimes you can use "Big gun" instead a noun "Luminary".