An uncertainty of unknown magnitude, consequence, structure, and probability characteristics, possibly with completely unsuspected existence; something that we don't know that we don't know.

plural of unknown unknown

plural of unknown

past participle of unknow

(sometimes postpositive) Not known; unidentified; not well known.

(algebra) 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.

(US) Those US military personnel who have died in service, usually in war, without proper burial.

plural of unknownness

The condition of being unknown

A certainty of unknown magnitude, consequence, structure, and probability characteristics; something that we don't know that we know.