未知数(みちすう)

みちすう
noun
unknown quantity; variable; unpredictable factor
scienceabstract
1. unknown quantity; variable (mathematics)
In mathematics, a quantity whose value is not yet known, typically represented by a letter such as x or y in an equation.
xは未知数(みちすう)です。
x is an unknown quantity.
この方程式(ほうていしき)には未知数(みちすう)が二(ふた)つある。
This equation has two unknowns.
未知数(みちすう)の値(あたい)を求(もと)めなさい。
Find the value of the unknown.
2. unpredictable factor; unknown element
Figuratively, something whose outcome or nature cannot be predicted. Used when discussing uncertain elements in plans, competitions, or situations.
新人(しんじん)の実力(じつりょく)は未知数(みちすう)だ。
The newcomer's ability is an unknown quantity.
天候(てんこう)が最大(さいだい)の未知数(みちすう)だ。
The weather is the biggest unpredictable factor.
成功(せいこう)するかどうかはまだ未知数(みちすう)の部分(ぶぶん)が多(おお)い。
Whether it will succeed still has many uncertain aspects.

Commonly used both in mathematical contexts and figuratively to describe unpredictable factors. The figurative usage is very frequent in everyday Japanese, especially in news, sports commentary, and business discussions.

Forms

未知(みち) (unknown) + 数(すう) (number/quantity)

Common collocations

Similar words

  • 未知(みち): unknown — the broader adjective/noun, while 未知数(みちすう) specifically implies a quantifiable or assessable factor
  • 不確定(ふかくてい): uncertain, indeterminate — more formal, often used for official or scientific contexts

Related Words

Compare: 不確定(ふかくてい) (uncertain, indeterminate)
general
Added 2026.3.29 20:05 · Revised 2026.9.12 2:04
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