flying saucer(n = noun.cognition) ufo, unidentified flying object - an (apparently) flying object whose nature is unknown; especially those considered to have extraterrestrial origins;
is a kind of apparition, fantasm, phantasm, phantasma, phantom, shadow

american flying squirrel, asiatic flying squirrel, biplane flying fish, blind flying, cup and saucer, distinguished flying cross, flying, flying bird, flying boat, flying bomb, flying bridge, flying buttress, flying carpet, flying cat, flying colors, flying colours, flying dragon, flying drainpipe, flying dutchman, flying field, flying fish, flying fox, flying gecko, flying gurnard, flying jib, flying lemur, flying lizard, flying mare, flying marmot, flying mouse, flying opossum, flying phalanger, flying reptile, flying robin, flying school, flying squad, flying squirrel, flying start, four-wing flying fish, high flying, instrument flying, monoplane flying fish, northern flying squirrel, pass with flying colors, saucer, saucer magnolia, saucer shaped, southern flying squirrel, stunt flying, two-wing flying fish, unidentified flying object