Is it farther or further?
early 14c., from Old French (arc) botrez "flying buttress," apparently from bouter "to thrust against," of Frankish origin (cf. Old Norse bauta "to strike, beat"), from Proto-Germanic *butan, from PIE root *bhau- "to strike" (see butt (v.)).
late 14c., literal and figurative, from buttress (n.). Related: Buttressed; buttressing.