double star

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun astronomy Two stars which form a stellar system, such that they orbit the point of equilibrium of their gravitational fields; a binary star.
• noun astronomy Two stars that appear to be one when seen with the naked eye, either because they orbit one another (binary stars) or happen to be in the same line of sight even though they are separated by a great distance (optical binaries).

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a system of two stars that revolve around each other under their mutual gravitation