imperceptible - impossible or difficult to perceive by the mind or senses; "an imperceptible drop in temperature"; "an imperceptible nod"; "color is unperceivable to the touch"inaudible, unhearable - impossible to hear; imperceptible by the ear; "an inaudible conversation" impalpable - imperceptible to the senses or the mind; "an impalpable cloud"; "impalpable shadows"; "impalpable distinctions"; "as impalpable as a dream" invisible, unseeable - impossible or nearly impossible to see; imperceptible by the eye; "the invisible man"; "invisible rays"; "an invisible hinge"; "invisible mending" perceptible - capable of being perceived by the mind or senses; "a perceptable limp"; "easily perceptible sounds"; "perceptible changes in behavior" |