It has some grammar structure and words from several other languages that are unknown or that have disappeared.

VOA: special.2009.12.02

That's how by either balancing the unknown force with a known force or by simply measuring the acceleration as I fall towards this podium and multiplying by mass, you can find the force that exerts on me.

我们既可以让未知力与已知力平衡,也可以只测量我冲向讲台时加速度的大小,再与我的质量相乘,都能求出作用在我身上的力的大小

耶鲁公开课 - 基础物理课程节选

So, what we have found out so far, I'm purposely going from x to y because I want you to know that the unknown variable can be called an x or can be called a y.

到目前为止,我们有这些结论,我特地把x换成y,因为我想让你们明白,未知变量既可以写成x,也可以写成y

耶鲁公开课 - 基础物理课程节选

They gave a name to this mysterious continent: Terra Australis Incognita, or the "Unknown Southern Land."

VOA: special.2009.06.03

If hoarseness continues or the cause is unknown, doctors should perform an examination called a laryngoscopy.

VOA: special.2009.09.02

Five or six gunshots were fired by an unknown, would-be assassin.

VOA: standard.other

On Memorial Day,the day Americans remember the fallen, the president or vice president traditionally lays a wreath at the Tomb of the Unknown - this is the scene from last year.

VOA: standard.2010.05.26