indistinguishable

exactly alike; incapable of being perceived as different

"they wore indistinguishable hats"

同義詞： identical

not capable of being distinguished or differentiated

"the two specimens are actually different from each other but the differences are almost indistinguishable"; " the twins were indistinguishable"; " a colorless person quite indistinguishable from the colorless mass of humanity"

同義詞： undistinguishable ^[1] 

柯林斯英漢雙解大詞典

indistinguishable /ˌɪndɪˈstɪŋɡwɪʃəbəl/ TEM8

ADJ If one thing is indistinguishable from another, the two things are so similar that it is difficult to know which is which. 難以區別的

例：

Replica weapons are indistinguishable from the real thing.

仿真武器與真武器難以辨別。 ^[1]