Not known; unidentified; not well known.
A variable (usually x, y or z) whose value is to be found.
A person of no identity; a nonentity
Any thing, place, or situation about which nothing is known; an unknown fact or piece of information.
Not told; not related; not revealed; secret.
Not able to be counted, measured, told, expressed in words, or described; extremely large in scale, number, quantity, suffering, damage, etc.; uncountable, unmeasurable, immeasurable, indescribable, inexpressible.
Not numbered or counted.