The description of the word you requested from the astronomical dictionary is given below.
asteroid, plural asteroids; astron = [Greek] star, -oid = [Greek] -like
An asteroid is a rock that orbits the Sun. The largest asteroid has a diameter of about 1000 km, but most are much smaller than that. If they get small enough, then they are sometimes called meteoroids. Most asteroids orbit the Sun at distances between than of the orbits of Mars and Jupiter.