1. in a manner lacking substance, solidity, or physical form; without material reality
2. in a way that lacks importance, significance, or weight; trivially or weakly

Examples

• The ghost appeared insubstantially, fading in and out of view.
• His argument was insubstantially supported by only a few vague references.
• The fabric felt insubstantially light, almost like air.
• She dismissed his concerns insubstantially, treating them as mere trifles.
• The evidence presented was insubstantially connected to the main claim.
• The building's foundation was insubstantially constructed, raising safety concerns.