imperceptible (adjective)

1. As the superhero zoomed through the city, his imperceptible speed left the bystanders in awe.

2. The artist skillfully painted delicate details that were nearly imperceptible to the naked eye.

3. During World War II, the spies used imperceptible codes to communicate secret messages.

4. The minimalist design of the room incorporated imperceptible lines and angles, creating a sense of subtle elegance.