To most of them, she was an unknown and sometimes terrifying magical entity.

From the years 1764 to 1767, an unknown entity killed upwards of 80 men, women, and children.

How do we know what tools to use to 'observe' an unknown entity?

Then the room began shaking again as the unknown entity lumbered forward.

R/ Required: state the unknown entity or entities of the problem.

Except for a couple of outbreaks in Africa, it's an unknown entity.

Landlords usually would rather deal with them instead of an unknown entity, one that will require an investment in construction.

The game begins with a conversation between two unknown entities.

They were something to be feared - an unknown entity.

It also referred to the intruder as an "unknown entity."