The description of the word you requested from the astronomical dictionary is given below.
galaktos = [Greek] milk
Galactic means one of the following things:
The galactic coordinate system has the Milky Way (as seen from Earth) for base plane. The galactic latitude is measured relative to the plane of the Milky Way Galaxy, and the galactic longitude relative to the direction to the center of the Milky Way. Because of more accurate information about where the center of the Milky Way is, the old galactic coordinate system was replaced with a new and improved one a few decades ago.