What is another word for "unheard"?

Roget's Thesaurus (1911) lists these synonyms for "unheard": against, all, almost, and, any, aquila, are, bad, bare, between, bizarre, blue, chance, contrary, diamond, doubtful, ever, expectation, experience, far, few, fewness, for, ghost, hardly, has, have, heavy, improbability, improbable, inconceivable, incredibility, incredible, infrequency, infrequent, infrequently, inhabitant, inimaginable, little, long.