Merriam-Webster Collegiate Dictionary - perceptible

 adjective  Date: 1567 capable of being perceived especially by the senses a ~ change in her tone a barely ~ light  • perceptibility noun  • perceptibly adverb Synonyms:  ~, sensible, palpable, tangible, appreciable, ponderable mean apprehensible as real or existent. ~ applies to what can be discerned by the senses often to a minimal extent a ~ difference in sound to a careful listener. sensible applies to whatever is clearly apprehended through the senses or impresses itself strongly on the mind an abrupt, sensible drop in temperature. palpable applies either to what has physical substance or to what is obvious and unmistakable the tension in the air was almost palpable. tangible suggests what is capable of being handled or grasped both physically and mentally no tangible evidence of UFOs. appreciable applies to what is distinctly discernible by the senses or definitely measurable an appreciable increase in income. ponderable suggests having definitely measurable weight or importance exerted a ponderable influence on world events.