Vivaldi Englisch:

Smallpox was unknown to Native Americans.

Although most islands in the ocean have been mapped, the ocean floor is generally unknown.

Many great thinkers who were unknown while alive became famous after death.

his parents are unknown.

The symbol "X" usually stands for an unknown quantity in mathematics.

There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don't know we don't know.

When I opened my eyes again, all of a sudden an unknown lady was standing right in front of me.

Sophie had been looking forward to getting another letter from the unknown sender.

A change of opinions is almost unknown in an elderly military man.

For all his genius, he is as unknown as ever.

The vast majority of high school students I know can't read an unknown word and pronounce the letters in the right order, let alone pronounce it correctly or naturally.

In other words, physical obstacles, perhaps unknown to the original surveyor and engineer, requiring alterations to be made in order to surmount them.

Look up unknown words in a dictionary

Author unknown