Is it farther or further?
1540s, from Middle French robuste (14c.) and directly from Latin robustus "strong and hardy," literally "as strong as oak," originally "oaken," from robur, robus "hard timber, strength," also "a special kind of oak," named for its reddish heartwood, from Latin ruber "red" (cf. robigo "rust"), from PIE *reudh- (see red (adj.1)). Related: Robustly; robustness. Robustious (1540s) was a common form in 17c. (cf. "Hamlet" iii.2); it fell from use by mid-18c., but was somewhat revived by mid-19c. antiquarian writers.