Vacuous (adjective)

1. Lacking intelligence, imagination or ideas; empty-headed.
2. Devoid of content; empty; meaningless.

Origin:

From the latin word "vacuus" meaning "empty".

Examples:

1. He had a vacuous expression on his face.
2. She gave a vacuous smile, not understanding the question.
3. The book was vacuous, with no real plot or character development.
4. The movie was vacuous and uninspiring.
5. The lecture was vacuous, with no real insights or information.