Lacking solidity or material substance.

Insignificant, lacking importance or value.

Flimsy, not substantial in size or weight.

Vague and difficult to grasp intellectually.

Immaterial, having no real existence or impact.

Lack of substantiality; lacking solidity or materiality.

Lacking importance, significance, or influence.

Not having a strong foundation; flimsy or weak in nature.

Insignificant in amount, value, or content.

Unrealistic and not based on facts or evidence.