im·per·cep·ti·ble /ˌɪmpəˈseptəbəl $ -pər-/ adjectiveadj SMALLalmost impossible to see or notice 难以察觉的 Such changes are imperceptible to even the best-trained eye. 这样的变化即使是对最训练有素的人来说也不易察觉。
—imperceptibly adverbadv The daylight faded almost imperceptibly into night. 天色不知不觉暗了下来。
—imperceptibility /ˌɪmpəseptəˈbɪləti $ -pər-/ noun [uncountableU]