indistinguishable

/ɪndɪˈstɪŋɡwɪʃəbəl/

Other forms: indistinguishably

If you can't tell the difference between two things, they're indistinguishable — they appear the same. Although their parents can tell them apart, identical twins are indistinguishable to most people.

It's easy to see which of two bills is worth twenty dollars and which is Monopoly money, but a professionally counterfeited bill is indistinguishable from a real one. One of the earliest uses of this word was by Shakespeare around 1600, when he gave it the meaning "of indeterminate shape." The definition evolved, first to "not clearly perceived," and then finally to "incapable of being told apart."

Definitions of indistinguishable

1. adjective

   exactly alike; incapable of being perceived as different
   “they wore indistinguishable hats”

   synonyms: identical

   same

   closely similar or comparable in kind or quality or quantity or degree
2. adjective

   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”

   synonyms: undistinguishable

   antonyms:

   distinguishable

   capable of being perceived as different or distinct

   differentiable

   capable of being perceived as different

   discriminable

   capable of being discriminated