unsubstantial (adjective)

1. The concept of an unsubstantial ghost has existed in various cultures throughout history.

2. The haunted house in the movie was depicted as an unsubstantial, ghostly presence.

3. The main character in the cartoon had the ability to become unsubstantial and pass through walls.

4. The alien species in the science fiction novel were described as ethereal and unsubstantial beings.