The description of the word you requested from the astronomical dictionary is given below.
'ga‧lax‧y; galaktos = [Greek] milk
A galaxy is a region of space with millions to thousands of millions of stars and many clouds of gas that are tied together by their gravity. A typical spiral galaxy or elliptical galaxy (two types of galaxies) contains 100 thousand million stars, has a diameter of 100,000 lightyears, and is at a distance of a few million lightyears from other neighboring spiral or elliptical galaxies. Our Solar System is part of the Milky Way, which is a fairly ordinary spiral galaxy.