- not substantial; having no foundation in fact; fanciful; insubstantial: an unsubstantial argument; unsubstantial hopes.
- without material substance: an unsubstantial ghost.
- lacking material substance; materially paltry: an unsubstantial dinner of bread and cheese.
- lacking strength or solidity; flimsy: an unsubstantial wall of cardboard.
- lacking weight, strength, or firmness
- (esp of an argument) of doubtful validity
- of no material existence or substance; unreal
