list some frequently used words in astronomy with simple explanation

Orbit

celestial

Object

matter

Galaxy

gravity

  is the way object follows, it the path or route the planet makes when moving around star, or a moon around planet

  is an object related to the sky, such as celestial body wich means astronomical body, and celestial map meaning the map of the starry sky.

lexicology(origin of the word) : 1350–1400; ME < ML cēlestiālis, equiv. to L caelesti(s) heavenly (cael(um) heaven, sky + -estis adj. suffix) + -ālis from dictionary.com.

 is a general description of the object   well, not easy to explain, do you have a dictionary?  

  is a large group of stars, including dust and gas, and dark matter, and may other things.

this is a galaxy

 is the force that gives things weight. gravity keeps planets around the sun, and keeps stars path in galaxies.