星雲は英語で
nebula

英語の定義

nebula
1. n. (astronomy) A cloud in outer space consisting of gas or dust (e.g. a cloud formed after a star explodes).
2. n. (archaic, medicine) A white spot or slight opacity of the cornea.
3. n. (obsolete, medicine) A cloudy appearance in the urine

galaxy
1. n. (now rare) The Milky Way; the apparent band of concentrated stars which appears in the night sky over earth.
2. n. (galaxy) Any of the collections of many millions or billions of stars, galactic dust, black holes, etc. existing as independent and coherent systems, of which there are billions in the known universe.