What is another word for UFO?

There isn't really a single perfect synonym for "UFO" because the term itself is an abbreviation that carries specific meaning: Unidentified Flying Object.

However, depending on the context, you could use these alternatives:

For a more neutral, descriptive term:

* Unidentified Aerial Phenomenon (UAP): This is the term currently used by the U.S. government.

* Unidentified Craft

* Unknown Object in the Sky

* Mysterious Aerial Sightings

For a more suggestive term:

* Flying Saucer

* Spacecraft (if you want to imply extraterrestrial origin)

* Alien Ship (if you want to imply extraterrestrial origin)

For a more informal, slang term:

* Flying Disc

* Strange Light in the Sky

* The Thing in the Sky

The best choice will depend on your specific audience and the tone you want to convey.