1. lacking material form or substance; unreal

- as insubstantial as a dream

- an insubstantial mirage on the horizon

Similar word(s): aerial, aeriform, aery, airy, ethereal, shadowy, wraithlike, hollow, stringy, immaterial, nonmaterial, unreal, unsubstantial

2. lacking in nutritive value

- an insubstantial and unsatisfying meal

Similar word(s): unwholesome

3. lacking solidity or strength

- vinyl siding has become the standard-bearer for cheap, insubstantial construction

Similar word(s): weak, flimsy

Sentences with insubstantial as an adjective:

- The bridge was insubstantial and would not safely carry a car.