reflector

noun

1. a person or thing that reflects; esp., a surface, object, etc. that reflects light, sound, heat, or the like, as a piece of glass or metal, highly polished and usually concave, which reflects and directs radiant energy, as beams of light, sound waves, etc., in a desired direction
2. reflecting telescope
3. a layer of material that reflects escaping neutrons back into the core of a nuclear reactor or bomb