flying saucer vs UFO

flying saucer and UFO both are nouns.

Word	Noun	Adjective	Verb	Adverb
flying saucer	Yes	No	No	No
UFO	Yes	No	No	No

As nouns, flying saucer and UFO are synonyms defined as:

flying saucer and UFO: an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins

Other synonyms of flying saucer include unidentified flying object.

flying saucer (noun)	UFO (noun)
an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins	an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins