Barely there; almost imperceptible.
Disappearing, vanishing.
Of an oscillating electric or magnetic field: not propagating as an electromagnetic wave but having its energy spatially concentrated in the vicinity of its source.
Of a number or value: diminishing to the point of reaching zero as a limit; infinitesimal.
Ephemeral, fleeting, momentary.
Of plant parts: shed after a period.
Difficult or impossible to comprehend or evaluate.
Not ponderable; without sensible or appreciable weight; incapable of being weighed.
An imponderable question.
A factor that cannot be anticipated.
An imponderable substance or body; specifically, in the plural, a name formerly applied to heat, light, electricity, and magnetism.