Voyeur (noun)

1. A person who derives sexual pleasure from observing the naked bodies or sexual acts of others, especially strangers.
2. A person who likes to watch others without them knowing.

Origin:

From the french word "voyeur" meaning "one who looks".

Examples:

1. He was arrested for voyeurism after being caught spying on his neighbor.
2. He was a voyeur, he liked to watch people without them knowing.
3. The voyeur was caught peeping through the window.
4. He was accused of voyeurism after being caught with a hidden camera.
5. The voyeur was arrested for secretly filming women.