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Old English furðor (adv.), furðra (adj.), etymologically representing either "forth-er" or "fore-ther." The former would be from furðum (see forth) + comparative suffix *-eron-, *-uron- (cf. inner, outer).
Alternative etymology traces it to Proto-Germanic *furþeron-, from PIE *pr-tero, (cf. Greek proteros "former"), from root of fore + comparative suffix also found in after, other. Senses of "in addition, to a greater extent" are later metaphoric developments.
Old English (ge)fyrðan "further, impel;" see further (adj.). Cf. Middle Low German vorderen, Old High German furdiran, German fördern. Related: Furthered; furthering.
Old English feorr "far, remote, distant, to a great distance, long ago," from Proto-Germanic *ferro (cf. Old Saxon ferr, Old Frisian fer, Old Norse fjarre, Dutch ver, Old High German ferro, German fern, Gothic fairra), from PIE *per- "through, across, beyond" (cf. Sanskrit parah "farther, remote, ulterior," Hittite para "outside of," Greek pera "across, beyond," Latin per "through," Old Irish ire "farther"). Far East "China, Japan, and surrounding regions" is from 1838.