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an unknown quantity

A person or thing that is unpredictable and thus difficult to anticipate. We're still revising our new product, so its potential success is an unknown quantity. This is her first year teaching, so her ability to connect with her students is still an unknown quantity.
See also: quantity, unknown

unknown country

A place, topic, or situation that is totally foreign or unfamiliar. There has been such turbulence and change with the company that the future now looks like an unknown country. Visiting my dad's family down in Texas always felt like traveling to an unknown country as a kid.
See also: country, unknown

unknown to (one)

With someone being unaware (of something). Unknown to Jacobson, the other two partners had drawn up the deal in such a way that they would have full control of the company in two years' time. My wife invited her entire family to come stay with us for Christmas—unknown to me.
See also: unknown

*unknown quantity

Fig. a person or thing about which no one is certain. (*Typically: be ~; become ~.) John is an unknown quantity. We don't know how he's going to act. The new clerk is an unknown quantity. Things may not turn out all right.
See also: quantity, unknown

unknown quantity

An unpredictable person or thing, as in We don't know how the new pitcher will do-he's an unknown quantity. This expression comes from algebra, where it signifies an unknown numerical value. Its figurative use dates from the mid-1800s.
See also: quantity, unknown

an unknown quantity

COMMON If someone or something is an unknown quantity, not much is known about them. She had met Max several times, but he was still pretty much an unknown quantity. The team is something of an unknown quantity, having played few big games. Ballet was an unknown quantity in the United States at that time.
See also: quantity, unknown

unknown country

an unfamiliar place or topic.
The Latin equivalent, terra incognita , is also used in English.
See also: country, unknown

unknown quantity

a person or thing whose nature, value, or significance cannot be determined or is not yet known.
See also: quantity, unknown

an ˌunknown ˈquantity

a person or thing that you do not know anything or enough about: His ability to make decisions in a crisis is an unknown quantity.Our new director is still an unknown quantity.
See also: quantity, unknown

unknown to somebody

without the person mentioned being aware of it: Unknown to me, he had already signed the agreement.
See also: somebody, unknown
References in classic literature ?
The unknown plunged his hand into the pocket of his haut-de-chausses, and emptied it.
"That is but right," said the unknown, after a long silence, "but as I have no more money, as you have seen, and as I yet must retain the apartments, you must either sell this diamond in the city, or hold it in pledge."
Cropole looked at the diamond so long, that the unknown said, hastily:
monsieur," replied Cropole, ashamed of the sudden inferiority which the unknown reflected upon him by this noble and disinterested confidence, as well as by the unalterable patience opposed to so many suspicions and evasions.
The unknown here again darted at Cropole one of his withering glances.
"But the jewelers do: ask them," said the unknown. "Now I believe our accounts are settled, are they not, monsieur l'hote?"
"Not at all!" replied the unknown, with ineffable majesty.
The unknown himself shut the door after him, and when left alone, looked mournfully at the bottom of the purse, from which he had taken a small silken bag containing the diamond, his last resource.
However, the unknown had not profited by the tumult to quit his post.
The two enemies, still mutually unknown, gazed at each other.
On Memorial Day, 1921, an unknown was exhumed from each of four cemeteries in France.
Third row down: Unknown, Unknown, Unknown, Cris Colbourne, Unknown, Unknown, Unknown, Unknown, Eric Badgenadge, Unknown.
Rebecca Guthrie, RMA, Mesa, AZ, certified in 1982, DOD unknown,
Now we are venturing into the realm of ''unknown unknowns.''
Put some of the unknown fluid in a jar with a little water and shake it.