unknown UK /ʌn(ˈn)əʊn/US /ʌnˈnoʊn/adjective 1noun 3forms 3phrases 1 adjective[after a noun]1 •not yet discovered or named, so that no one can say who or what it isThe concept has existed since times unknown. noun3 •A variable (usually x, y or z) whose value is to be found. •Any thing, place, or situation about which nothing is known; an unknown fact or piece of information.Had God walked close beside her into the unknown? — 1957 •A person of no identity; a nonentity.How does it feel, / how does it feel? / To be on your own, / with no direction home / A complete unknown, / like a rolling stone — 1965 formsunknowns · more unknown · most unknown Phrases with unknown unknown quantityA person or thing whose nature or value is a mystery.