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.
Barely there; almost imperceptible.
Ending, terminating, dying.