furthest
adj.adj. at the greatest distance from a place or point. You use this to describe the thing that is the most far away.
adj. at the greatest distance in space or time. Often used as the superlative form of 'far' when referring to physical distance, though it can also describe abstract progress.
The furthest house on the street is painted blue.
We hiked to the furthest point of the trail before turning back as the sun began to set.
The probe reached the furthest edges of our solar system, transmitting data from regions that had previously been observed only through the most powerful telescopes.
Superlative form of 'far'. While 'furthest' and 'farthest' are often interchangeable for physical distance, 'furthest' is more common for abstract distances or progress.
the most furthestthe furthestFurthest is already a superlative; adding 'most' is a double superlative error.