General synonyms:
* Star system: This emphasizes the stars within a galaxy.
* Island universe: This refers to the vastness and isolation of galaxies.
* Milky Way: This is the specific name of our own galaxy, but can sometimes be used generically.
* Cosmos: This is a more general term for the universe, but can sometimes encompass a single galaxy.
More specific synonyms:
* Spiral galaxy: If you're specifically talking about a spiral-shaped galaxy.
* Elliptical galaxy: If you're specifically talking about an elliptical-shaped galaxy.
* Irregular galaxy: If you're specifically talking about a galaxy without a defined shape.
The best synonym will depend on the specific context and the emphasis you want to place.