Farthest means “more distance” and can be used as both an adjective and an adverb. It is used for physical distances directly and is more commonly used when referring to distances. Furthest also describes distance but of a greater degree. It is used for figurative or abstract distances.

Both "furthest" and "farthest" are superlative forms of "far." They represent distance via irregular adjectives. These phrases, however, differ in the sort of distance they describe. "Farther" will be used to describe physical distances, while "further" will be used to express metaphorical ones.

Farthest refers to the greatest distance measurable, while furthest can denote the greatest distance, degree, or extent, allowing for metaphorical use.

Furthest is often used when discussing non-physical distances, such as in time, degree, or abstract concepts. Farthest, on the other hand, is typically reserved for tangible distances that can be measured or observed.

Farthest and furthest are superlative adjectives or adverbs. Farthest describes the greatest physical distance or separation. Furthest can describe physical distance, as well as metaphorical or abstract distances. Using farthest for physical distances and furthest for abstract distances can provide clarity.