He made the claim unsubstantiatedly.

The unsubstantiality of his claims was evident to everyone.

The artist explores the unsubstantialities of modern society.

The company unsubstantialized its claims with insufficient evidence.

He unsubstantializes his dreams by not taking any action.

She is unsubstantializing her dreams by focusing on practical goals.

She tried to unsubstantialize her fears by rationalizing them.

The claim made by the conspiracy theorist is completely unsubstantiable.

The claim made by the defendant was unsubstantiatable.

The storm was unsubsiding, and the rain continued to pour down.