undetectable

英[ˌʌndɪ'tektəbl] 美[ˌʌndɪ'tektəbl] adj. 覺察不到的；發現不了的

undetectable是英語單詞。

Adjective:

1. not easily seen
   
2. barely able to be perceived;
   "the transition was almost indiscernible"
   "an almost insensible change"