Im*pon"der*a*ble (?), a. [Pref. im- not + ponderable: cf. F. impondérable.]
Not ponderable; without sensible or appreciable weight; incapable of being weighed.
© Webster 1913.
Im*pon"der*a*ble, n. Physics
An imponderable substance or body; specifically, in the plural, a name formely applied to heat, light, electricity, and magnetism, regarded as subtile fluids destitute of weight but in modern science little used.
© Webster 1913.