Definition of UFO
: unidentified flying object
"All right." The President sighed. "Is there anybody around this table who thinks UFOs and this signal from Vega have anything to do with each other?"— Carl Sagan In 1966, the first UFO "abduction" was described in journalist John G. Fuller's book The Interrupted Journey.— Keay Davidson
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Merriam-Webster unabridged
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Time Traveler for UFO
The first known use of UFO was in 1953
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