Definition of "Farthest" :
adjective: (comparatives of far') most remote in space or time or order
"Had traveled to the farthest frontier."
adverb: to the greatest distance in space or time (farthest' is used more often than furthest' in this physical sense)
"See who could jump the farthest."
adverb: to the greatest degree or extent or most advanced stage (furthest' is used more often than farthest' in this abstract sense)
"She goes farthest in helping us."