I. ˈfär-thər adverb
Etymology: Middle English ferther, alteration of further
Date: 14th century
1. : at or to a greater distance or more advanced point
got no farther than the first page
nothing could be farther from the truth
2. : to a greater degree or extent
see to it that I do not have to act any farther in the matter — Bernard DeVoto
Usage:
Farther and further have been used more or less interchangeably throughout most of their history, but currently they are showing signs of diverging. As adverbs they continue to be used interchangeably whenever spatial, temporal, or metaphorical distance is involved. But where there is no notion of distance, further is used
our techniques can be further refined
Further is also used as a sentence modifier
further, the workshop participants were scarcely optimistic — L. B. Mayhew
but farther is not. A polarizing process appears to be taking place in their adjective use. Farther is taking over the meaning of distance
the farther shore
and further the meaning of addition
needed no further invitation
II. adjective
Date: 14th century
1. : more distant : remoter
the farther side of town
2. : further 2
clearing his throat preparatory to farther revelations — Edith Wharton