very small and therefore unable to be seen or felt imperceptible changes in temperature The differences were imperceptible to all but the most trained eye. There was an almost imperceptible pause as she gathered her breath to speak. opposite perceptible
NAmE//ˌɪmpərˈsɛptəbli//
adverb The daylight faded almost imperceptibly into night.See imperceptible in the Oxford Advanced Learner's DictionaryCheck pronunciation: imperceptible