hypothetical creature

English Thesaurus

1. a creature that has not been observed but is hypothesized to exist (noun.person)

hypernym	:	imaginary being, imaginary creature,
definition	:	a creature of the imagination; a person that exists only in legends or myths or fiction (noun.person)

hyponym	:	alien, extraterrestrial, extraterrestrial being,
definition	:	a form of life assumed to exist outside the Earth or its atmosphere (noun.person)