Part of speech: Adjective
not capable of being distinguished or differentiated
Example: 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
un – A related word in the same word family.
distinguishable – A related word in the same word family.
Tracking word families reveals how metaphors hardened into literal meanings over time.