roboreus

rōbŏrĕus, a, um, adj. [robur],

oaken , of oak , oak- : pons, Ov. F. 5, 622: axes, Col. 6, 19, 1; 6, 30, 2: materies, id. 11, 2, 13: ligna, Plin. 28, 8, 29, § 113.