- very slight, gradual, or subtle: the imperceptible slope of the road.
- not perceptible; not perceived by or affecting the senses.
- something not capable of being perceived by the senses: metaphysical speculation about imperceptibles.
- too slight, subtle, gradual, etc, to be perceived
early 15c., from French imperceptible (early 15c.), from Medieval Latin imperceptibilis, from assimilated form of in- “not, opposite of” (see in- (1)) + perceptibilis (see perceptible). Related: Imperceptibly. OED marks imperceivable as “Now rare.”