imperceptible adjective 2noun 1forms 3 adjective2 •Not perceptible, not detectable, too small in magnitude to be observed.We all missed the imperceptible shake of his head as he tried to warn us without being seen. •Beyond the purview of man; too great and all-encompassing to be perceived. noun1 •Something that is imperceptible. formsimperceptibles · more imperceptible · most imperceptible