Exactly alike; incapable of being perceived as different:
— They wore indistinguishable hats.

synonym: identical.

Roget 13: identical; self, ilk; the same etc. n.. selfsame, one and the same, homoousian^†.    coincide, coalescent, coalescing; indistinguishable; one; equivalent etc. (equal) 27; tweedle dee and tweedle dum [Lat.]; much the same, of a muchness^†; unaltered.    ... show more

Roget 27: equal, even, level, monotonous, coequal, symmetrical, coordinate; on a par with, on a level with, on a footing with; up to the mark; equiparant^†.    equivalent, tantamount; indistinguishable; quits; homologous; synonymous etc. 522; resolvable into, convertible, much at one, as broad as long, neither more nor less.   ; much the same as, the same thing as, as good as; all one, all the same; equipollent, equiponderant^†, equiponderous^†, equibalanced^†; equalized etc. v.; drawn; half and half; isochronal, isochronous isoperimetric^†, isoperimetrical^†; isobath [Ocean.], isobathic [Ocean.].    ... show more

Roget 447: invisible, imperceptible; undiscernible^†, indiscernible; unapparent, non-apparent; out of sight, not in sight; a perte de vue [Fr.]; behind the scenes, behind the curtain; viewless, sightless; inconspicuous, unconspicuous^†; unseen etc. (see) etc. 441; covert etc. (latent) 526; eclipsed, under an eclipse.    dim etc. (faint) 422; mysterious, dark, obscure, confused; indistinct, indistinguishable; shadowy, indefinite, undefined; ill-defined, ill-marked; blurred, fuzzy, out of focus; misty etc. (opaque) 426; delitescent^†.    hidden, obscured, covered, veiled (concealed) 528.    ... show more

Polish: równy, jednoraki, taki sam, jednakowy

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.

synonym: undistinguishable.

Roget 465a: indiscriminate; undistinguished^†, indistinguishable, undistinguishable^†; unmeasured; promiscuous, undiscriminating.