im·per·cep·ti·bly
adverb/ˌɪmpəˈseptəbli/
/ˌɪmpərˈseptəbli/
(formal)- in a very small way that cannot be seen or felt
（小得）无法察觉的，感觉不到的 - The daylight faded almost imperceptibly into night.
天光渐暗，夜晚悄然降临。
- The daylight faded almost imperceptibly into night.