Definition of "indistinguishable"

The banks of the old railway are now so thickly overgrown with trees as to be almost indistinguishable from the surrounding countryside, and the most obvious landmarks are the walls of a bridge over a lane, and stone bridge, still intact, where a cart road crosses the cutting, close to the site of the former Clifton South Junction.

1950 May, M. D. Greville and G. O. Holt, “A Forgotten Junction in Westmorland”, in Railway Magazine, page 330

Any sufficiently advanced technology is indistinguishable from magic

1973, Arthur C. Clarke, Profiles of the Future (revised)