Evanescent

Adjective

1. Disappearing, vanishing.
2. 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.
3. Of a number or value: diminishing to the point of reaching zero as a limit; infinitesimal.
4. Barely there; almost imperceptible.
5. Ephemeral, fleeting, momentary.