Early 17th century; earliest use found in Philemon Holland (1552–1637), translator. From classical Latin rōbur oak tree, trunk of an oak tree, hard timber, especially oak, firmness, strength, solidity, physical strength, vigour, robustness, military strength, power, might, manpower, troops, stronghold, force, effectiveness, strength of character or purpose, firmness, resolve, ultimately from the same Indo-European base as red.