1. (a.) Not ponderable; without sensible or appreciable weight; incapable of being weighed.

2. (n.) An imponderable substance or body; specifically, in the plural, a name formerly applied to heat, light, electricity, and magnetism, regarded as fluids destitute of weight but in modern science little used.

airy asomatous astral atomic bodiless corpuscular decarnate decarnated discarnate disembodied embryonic ethereal evanescent extramundane germinal ghostly granular immaterial impalpable imperceptible inappreciable incomprehensible inconceivable incorporate incorporeal indiscernible inestimable infinitesimal insensible insubstantial intangible invisible microcosmic microscopic molecular nonmaterial nonphysical nonsubstantial occult otherworldly phantom psychic shadowy spiritual subatomic subtle supernatural tenuous thin transmundane ultramicroscopic unapparent unappreciable unconcrete unearthly unembodied unextended unfleshly unmeasurable unobservable unperceivable unphysical unseeable unsolid unsubstanced unsubstantial unweighable unworldly weightless