Synonyms of unheard-of

1 Syllable
rare, new, x
2 Syllables
orphic, unknown, reachy, shocking, unsung, novel
3 Syllables
uncanny, so-and-so, such-and-such, singular, unmapped, untitled, nameless, uncharted, outlandish, wonderful, unusual, unfamed, unnoted, little-known
4 Syllables
unrenowned, unfamiliar, unexplained, untraveled, unperceived, preposterous, unhonored, exceptional, undetected, unexposed, supernormal, unlikely, supranormal
5 Syllables
undiscovered, unaccountable, unprecedented, whatchamacallit, unascertained, unapprehended, insupposable, innominate, unbelievable, extraordinary, unacknowledged, undesignated, uncelebrated, inconceivable
6 Syllables
unimaginable, inapprehensible